基本情報

所属

• 理学研究院　物理学部門　電子物性物理学分野

職名

• 教授

学位

• 理学博士（名古屋大学）

ホームページURL

https://kaken.nii.ac.jp/d/r/60251691.ja.html

J-Global ID

• 201501050293675255

研究キーワード

• 超伝導   有機超伝導体   強相関電子系   ナイトシフト   高圧   有機伝導体   圧力下NMR   高速AD変換システム   反強磁性   磁場誘起金属絶縁体転移   電荷秩序   部分重水素置換   核四極子   Mott境界   TTF=TCNQ   誘電物性   p-d相互作用   同位体置換   角度依存   圧力   NMR   BEDT-TTF   FFLO   13C-NMR   ^<13>C   TMTSF   133C-NMR   DCNQI   SDW   

研究分野

• ナノテク・材料 / 有機機能材料

担当教育組織

•  学士課程　理学部
•  修士課程　理学院
•  博士課程　理学院

職歴

• 2012年 - 2013年 北海道大学 理学(系)研究科(研究院) 教授

所属学協会

• 日本物理学会   

研究活動情報

論文

• Thermodynamic properties of the Mott insulator-metal transition in a triangular lattice system without magnetic order

  Emre Yesil, Shusaku Imajo, Satoshi Yamashita, Hiroki Akutsu, Yohei Saito, Andrej Pustogow, Atsushi Kawamoto, Yasuhiro Nakazawa

  PHYSICAL REVIEW B 107 4 2023年01月 

  The organic system K-[(BEDT-TTF)1_x(BEDT-STF)x]2Cu2(CN)3, showing a Mott transition between a nonmagnetic Mott insulating (NMI) state and a Fermi liquid (FL), is systematically studied using calorimetric measurements. An increase in the electronic heat capacity at the transition from the NMI state to the FL state which keeps the triangular dimer lattice demonstrates that the charge sector lost in the Mott insulating state is recovered in the FL state. We observed that the remaining low-energy spin excitations in the Mott insulating state show a unique temperature dependence and that the NMI state has a larger lattice entropy originating from the frustrated lattice, which leads to a Pomeranchuk-like effect on the electron localization. Near the Mott boundary, an unexpected enhancement and magnetic field dependence of the heat capacity are observed. This anomalous heat capacity is different from the behavior in a typical first-order Mott transition and shows similarities with quantum critical behavior. To reconcile our results with previously reported scenarios about a spin gap and the first-order Mott transition, further studies are desired.
• Dynamics of ethylene groups and hyperfine interactions between donor and anion molecules in λ -type organic conductors studied by Ga69,71 -NMR spectroscopy

  N. Yasumura, T. Kobayashi, H. Taniguchi, S. Fukuoka, A. Kawamoto

  Physical Review B 2022年12月05日 [査読有り]
  
• Antiferromagnetic ordering of organic Mott insulator λ−(BEDSe-TTF)2GaCl4

  A. Ito, T. Kobayashi, D. P. Sari, I. Watanabe, Y. Saito, A. Kawamoto, H. Tsunakawa, K. Satoh, H. Taniguchi

  Physical Review B 106 4 2022年07月12日
• Relationship between electronic inhomogeneity and bandwidth in the organic conductor κ−(BEDT−TTF)2Cu[N(CN)2]I studied by C13 NMR spectroscopy

  T. Kobayashi, A. Suzuta, A. Kawamoto

  Physical Review B 2022年05月31日
• C13 NMR study of the stabilization of the antiferromagnetic ground state and the emergence of unconventional magnetic state in a molecular π−d system

  S. Fukuoka, Y. Ito, Y. Ihara, A. Kawamoto

  Physical Review B 105 13 2022年04月25日
• Magnetic state in the quasi-two-dimensional organic conductor λ−(BEST)2FeCl4 and the path of π−d interaction

  Rikumaru Saito, Youhei Iida, Takuya Kobayashi, Hiromi Taniguchi, Noriaki Matsunaga, Shuhei Fukuoka, Atsushi Kawamoto

  Physical Review B 105 16 2022年04月11日
• Antiferromagnetic Ground State of Molecular π-d System λ-(BEDT-STF)2FeCl4 Studied by Site-Selective Magnetization and Thermodynamic Measurements

  Shuhei Fukuoka, Atsushi Kawamoto

  Chemistry Letters 2022年02月01日
• Rise and fall of Landau’s quasiparticles while approaching the Mott transition

  Andrej Pustogow, Yohei Saito, Anja Löhle, Miriam Sanz Alonso, Atsushi Kawamoto, Vladimir Dobrosavljević, Martin Dressel, Simone Fratini

  Nature Communications 12 1 2021年12月 

  Landau suggested that the low-temperature properties of metals can be understood in terms of long-lived quasiparticles with all complex interactions included in Fermi-liquid parameters, such as the effective mass m(star). Despite its wide applicability, electronic transport in bad or strange metals and unconventional superconductors is controversially discussed towards a possible collapse of the quasiparticle concept. Here we explore the electrodynamic response of correlated metals at half filling for varying correlation strength upon approaching a Mott insulator. We reveal persistent Fermi-liquid behavior with pronounced quadratic dependences of the optical scattering rate on temperature and frequency, along with a puzzling elastic contribution to relaxation. The strong increase of the resistivity beyond the Ioffe-Regel-Mott limit is accompanied by a 'displaced Drude peak' in the optical conductivity. Our results, supported by a theoretical model for the optical response, demonstrate the emergence of a bad metal from resilient quasiparticles that are subject to dynamical localization and dissolve near the Mott transition.
• Spin density wave in the strongly dimerized quasi-one-dimensional organic conductor (DMET-TTF) 2AuBr2

  Youhei Iida, Masashi Sawada, Yoshiaki Sasaki, Tomoaki Tsuchiya, Takaaki Minamidate, Noriaki Matsunaga, Atsushi Kawamoto, Kazushige Nomura

  Physical Review B 104 18 2021年11月04日 

  At ambient pressure, studies of resistivity, magnetic susceptibility, and carbon-13 nuclear magnetic resonance (NMR) were conducted on the quasi-one-dimensional organic conductor (DMET-TTF)(2)AuBr2. Resistivity measurements showed a broad minimum at approximately 160 K, and the insulator behavior below this temperature and magnetic susceptibility results revealed a dip structure at 22 K. At the same temperature, a sharp peak in the temperature dependence of T-1(-1) associated with the antiferromagnetic (AFM). transition was found, along with drastic splitting of the NMR spectra, indicating a commensurate AFM structure. The amplitude of the magnetic moments was determined to be 0.06 mu(B)/molecule from the hyperfine coupling constant tensor and the angular dependence of the internal field in the AFM phase. The small magnetic moment signifies the AFM nesting type, i.e., commensurate spin density wave. An antiferromagnetic ordering of (up arrow up arrow down arrow down arrow) along the one-dimensional chain is expected from the 2k(F) instability. This behavior can be explained by the strong dimerization of the one-dimensional DMET-TTF chain.
• Dielectric Anomaly and Charge Fluctuations in the Non-Magnetic Dimer Mott Insulator λ-(BEDT-STF)2GaCl4

  Olga Iakutkina, Roland Rosslhuber, Atsushi Kawamoto, Martin Dressel

  Crystals 11 9 1031 - 1031 2021年08月27日 

  The dimer Mott insulator lambda-(BEDT-STF)(2)GaCl4 undergoes no magnetic order down to the lowest temperatures, suggesting the formation of a novel quantum disordered state. Our frequency and temperature-dependent investigations of the dielectric response reveal a relaxor-like behavior below T approximate to 100 K for all three axes, similar to other spin liquid candidates. Optical measurement of the charge-sensitive vibrational mode nu(27)(b(1u)) identifies a charge disproportionation Delta rho approximate to 0.04e on the dimer that exists up to room temperature and originates from inequivalent molecules in the weakly coupled dimers. The linewidth of the charge sensitive mode is broader than that of typical organic conductors, supporting the existence of a disordered electronic state.
• Pressure-Tuned Superconducting Dome in Chemically-Substituted κ-(BEDT-TTF)2Cu2(CN)3

  Yohei Saito, Anja Löhle, Atsushi Kawamoto, Andrej Pustogow, Martin Dressel

  Crystals 11 7 817 - 817 2021年07月14日 

  The quantum spin liquid candidate kappa-(BEDT-TTF)(2)Cu-2(CN)(3) has been established as the prime example of a genuine Mott insulator that can be tuned across the first-order insulator-metal transition either by chemical substitution or by physical pressure. Here, we explore the superconducting state that occurs at low temperatures, when both methods are combined, i.e., when kappa-[(BEDT-TTF)(1-x)(BEDT-STF)(x)](2)Cu-2(CN)(3) is pressurized. We discovered superconductivity for partial BEDT-STF substitution with x = 0.10-0.12 even at ambient pressure, i.e., a superconducting state is realized in the range between a metal and a Mott insulator without magnetic order. Furthermore, we observed the formation of a superconducting dome by pressurizing the substituted crystals; we assigned this novel behavior to disorder emanating from chemical tuning.
• Charge imbalance in λ−(BETS)2GaCl4 and their interplay with superconductivity

  Olga Iakutkina, Ece Uykur, Takuya Kobayashi, Atsushi Kawamoto, Martin Dressel, Yohei Saito

  Physical Review B 104 4 2021年07月06日 

  The two-dimensional organic superconductor lambda-(BETS)(2)GaCl4 exhibits pronounced charge fluctuations below T approximate to 150 K, in contrast to the sibling compound kappa-(BETS)(2)GaCl4 that remains metallic down to milli-Kelvin. Infrared spectroscopy reveals only minor splitting in the vibrational features of the latter compound, common to other strongly dimerized kappa-type salts. When the organic molecules are arranged in the A-type pattern, however, a strong vibrational nu(27)(b(1u)) mode is present that forms a narrow doublet. Most important, when cooling lambda-(BETS)(2)GaCl4 below 150 K, two weak side modes appear due to charge disproportionation that amounts to 2 delta = 0.14e. In analogy to the beta ''-type organic conductors, we propose that charge fluctuations play an important role in emerging of unconventional superconductivity in lambda-(BETS)(2)GaCl4 at T-c = 4.7 K. We discuss the possibility of a charge-density wave that coexists with the proposed spin-density-wave state.
• Effects of Anion Substitution on Unconventional Antiferromagnetic Ground State of Molecular π–d System λ-(BEDT-STF)2FexGa1−xCl4

  Shuhei Fukuoka, Kaduki Haruyama, Yoshihiko Ihara, Atsushi Kawamoto

  Journal of the Physical Society of Japan 90 4 043702 - 043702 2021年04月15日 

  lambda-type molecular pi-d systems are coupled systems consisting of pi electron systems with strong magnetic interactions and 3d electron systems with weak magnetic interactions. They exhibit an unconventional antiferromagnetic ground state in which the 3d spins behave as if they remain paramagnetic even below T-N. In this study, we investigated the anion substitution effects of lambda-(BEDT-STF)(2)FexGa1-xCl4 by heat capacity measurements. A Schottky-type anomaly was observed for all alloy compounds (0.1 <= x <= 1.0). We found that the exchange field, which is the origin of this Schottky-type anomaly, decreases with the Fe content. Based on these results, we discuss the role of each magnetic interaction involved in the stabilization of the antiferromagnetic ground state and emergence of paramagnetic-like behavior.
• Enhancement of electron correlations and spin density wave fluctuations of the organic superconductor λ−(BETS)2GaCl4 under pressure proved by C13 NMR

  M. Sawada, A. Kawamoto, T. Kobayashi

  Physical Review B 103 4 2021年01月11日
• Chemical tuning of molecular quantum materials κ-[(BEDT-TTF)1−x(BEDT-STF)x]2Cu2(CN)3: from the Mott-insulating quantum spin liquid to metallic Fermi liquid

  Yohei Saito, Roland Rösslhuber, Anja Löhle, Miriam Sanz Alonso, Maxim Wenzel, Atsushi Kawamoto, Andrej Pustogow, Martin Dressel

  Journal of Materials Chemistry C 9 33 10841 - 10850 2021年 

  The electronic properties of molecular conductors can be readily varied via physical or chemical pressure as it enlarges the bandwidth W. This enables them to cross the Mott insulator-to-metal phase transition by reducing electronic correlations U/W. Here we introduce an alternative path by spatially expanding the molecular orbitals when partially replacing sulfur by selenium in the constituting bis-(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) molecules of the title compound. We characterize how the insulating quantum-spin-liquid state is tuned via a Mott transition to the metallic Fermi-liquid state crossing a narrow region of superconductivity. The transport, dielectric, and optical measurements reveal that at this first-order phase transition, metallic regions coexist in the insulating matrix leading to pronounced percolative effects, which are most obvious in the strong enhancement of the dielectric constant at low temperatures.
• Interacting electron spins in κ−(BEDT-TTF)2Cu[N(CN)2]I investigated by ESR spectroscopy

  Lena Nadine Majer, Björn Miksch, Olga Iakutkina, Takuya Kobayashi, Atsushi Kawamoto, Martin Dressel

  Physical Review B 102 21 2020年12月24日 

  We performed angular and temperature-dependent electron-spin-resonance measurements in the quasi-two-dimensional organic conductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]I. The interlayer spin diffusion is much weaker compared to the Cl and Br analogs, which are antiferromagnetic insulator and paramagnetic metal, respectively;kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]I behaves insulating when cooled below T = 200 K. A spin gap (Delta approximate to 18 K) opens at low temperatures leading to a spin-singlet state. Due to intrinsic disorder a substantial number of spins (similar to 1%) remains unpaired. We observe additional signals below T = 4 K with a pronounced anisotropy indicating the presence of local magnetic moments coupled to some fraction of those unpaired spins.
• Selective observation of spin and charge dynamics in an organic superconductor λ−(BETS)2GaCl4 using Ga69,71 NMR measurements

  T. Kobayashi, K. Tsuji, A. Ohnuma, A. Kawamoto

  Physical Review B 2020年12月15日
• Charge disproportionation in the spin-liquid candidate κ−(ET)2Cu2(CN)3 at 6 K revealed by Cu63 NQR measurements

  T. Kobayashi, Q.-P. Ding, H. Taniguchi, K. Satoh, A. Kawamoto, Y. Furukawa

  Physical Review Research 2020年10月30日
• Thermodynamic Investigation on Antiferromagnetic Ordered State of the Molecular π–d System λ-(BEDT-STF)2FeCl4

  Shuhei Fukuoka, Takaaki Minamidate, Noriaki Matsunaga, Yoshihiko Ihara, Atsushi Kawamoto

  Journal of the Physical Society of Japan 89 7 073704 - 073704 2020年07月15日 [査読有り][通常論文]
   

  We performed heat capacity measurements on the molecular pi-d system lambda-(BEDT-STF)(2)FeCl4 to discuss the unconventional paramagnetic-like behavior. We observed a Schottky-type anomaly below T-N of 16 K which is inherent in the 3d spin degrees of freedom as is observed in lambda-(BETS)(2)FeCl4. This result suggests that the paramagnetic-like behavior is not a unique behavior in lambda-(BETS)(2)FeCl4 but a universal behavior in lambda-type pi-d systems. In the case of lambda-(BETS)(2)FeCl4, a metal-insulator (M-1) transition occurs simultaneously with the antiferromagnetic transition at T-N of 8.3 K, and the paramagnetic-like behavior is observed below T-N. Because lambda-(BEDT-STF)(2)FeCl4 is insulating over the entire temperature range, our results revealed that the M-I transition is not essential for the emergence of the paramagnetic-like behavior. By comparing the thermodynamic nature of lambda-(BEDT-STF)(2)FeCl4 and lambda-(BETS)(2)FeCl4, we discuss the possible origin of the paramagnetic-like behavior.
• Selective observation of sublattice magnetization in the molecular π−d system λ−(BEDT−STF)2FeCl4 studied by C13 NMR

  S. Fukuoka, T. Minamidate, Y. Ihara, A. Kawamoto

  Physical Review B 101 18 2020年05月01日 [査読有り][通常論文]
  
• Spin-density wave in the vicinity of superconducting state in λ−(BETS)2GaBrxCl4−x probed by C13 NMR spectroscopy

  T. Kobayashi, T. Ishikawa, A. Ohnuma, M. Sawada, N. Matsunaga, H. Uehara, A. Kawamoto

  Physical Review Research 2020年04月24日 [査読有り][通常論文]
  
• C13–NMR study of charge fluctuations in α–(BEDT–TTF)MX salts (M=alkali metal; X=S, Se)

  Akihiro Ohnuma, Atsushi Kawamoto

  Physical Review B 100 24 2019年12月04日 

  Optical studies of the density wave (DW) salt of alpha-(BEDT-TTF)(2)KHg(SCN)(4) revealed a pseudo- gap due to a charge fluctuation below T* similar or equal to 200 K. Moreover, C-13-NMR studies of the DW salt of alpha-(BEDT-TTF)(2)RbHg(SCN)(4) and of the superconductivity (SC) salt of alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4) suggested that the NMR line width of the A site increased and the charge disproportionation in the A column developed below T*. These phenomena may be due to the development of a horizontal stripe modulation of the local charge density. However, whether the horizontal stripe modulation develops or not and the relationships among T* anomalies, the pseudogap, and line broadening, were unclear. In this study, C-13-NMR measurements were obtained of the metallic salt of alpha-(BEDT-TTF)(2)T1Hg(SeCN)(4), and its electronic structure was compared with those of the DW and SC salts. The NMR line width of the A site and chi(B)/chi(C) in Rb(SCN) and NH4(SCN) increased and deviated from that in T1(SeCN) below T*, suggesting the development of the instability of horizontal stripe modulation in Rb(SCN) and NH4 (SCN) and that T* anomalies could be due to the instability.
• Inhomogeneous electronic state of organic conductor κ−(BEDT-TTF)2Cu[N(CN)2]I studied by C13 NMR spectroscopy

  T. Kobayashi, A. Suzuta, K. Tsuji, Y. Ihara, A. Kawamoto

  Physical Review B 100 19 195115  American Physical Society ({APS}) 2019年11月 [査読有り][通常論文]
  
• Microscopic coexistence of superconductivity and charge order in the organic superconductor beta"-(BEDT-TTF)(4)[(H3O)Ga(C2O4)(3)]center dot C6H5NO2

  Ihara Y, Moribe K, Fukuoka S, Kawamoto A

  PHYSICAL REVIEW B 100 6 2019年08月20日 [査読有り][通常論文]
   

  The electron paramagnetic resonance study for an organic superconductor $\beta''$-(BEDT-TTF)$_{4}$[(H$_3$O)Ga(C$_2$O$_4$)$_3$]$\cdot$C$_6$H$_5$NO$_2$ reveals that superconductivity coexists uniformly with the charge ordered state in one material. In the charge ordered state, the interplane spin exchange is gapped, while the in-plane conductivity is not significantly modified. This anisotropic behavior is explained by the exotic charge ordered state, in which molecular-site selective carrier localization coexists with conducting carriers on other molecules. Relationship between superconductivity and this conductive charge ordered state is investigated.
• Gap Symmetry of the Organic Superconductor lambda-(BETS)(2)GaCl4 Determined by Magnetic-Field-Angle-Resolved Heat Capacity

  Imajo Shusaku, Yamashita Satoshi, Akutsu Hiroki, Kumagai Hiroya, Kobayashi Takuya, Kawamoto Atsushi, Nakazawa Yasuhiro

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 88 2 2019年02月15日 [査読有り][通常論文]
  
• Magnetic and Electronic Properties of pi-d Interacting Molecular Magnetic Superconductor kappa-(BETS)(2)FeX4 (X = Cl, Br) Studied by Angle-Resolved Heat Capacity Measurements

  Fukuoka Shuhei, Fukuchi Sotarou, Akutsu Hiroki, Kawamoto Atsushi, Nakazawa Yasuhiro

  CRYSTALS 9 2 2019年02月 [査読有り][通常論文]
   

  Thermodynamic picture induced by pi-d interaction in a molecular magnetic superconductor kappa-(BETS)(2)FeX4 (X = Cl, Br), where BETS is bis(ethylenedithio)tetraselenafulvalene, studied by single crystal calorimetry is reviewed. Although the S = 5/2 spins of Fe3+ in the anion layers form a three-dimensional long-range ordering with nearly full entropy of Rln6, a broad hump structure appears in the temperature dependence of the magnetic heat capacity only when the magnetic field is applied parallel to the a axis, which is considered as the magnetic easy axis. The scaling of the temperature dependence of the magnetic heat capacity of the two salts is possible using the parameter of |J(dd)|/k(B) and therefore the origin of the hump structure is related to the direct magnetic interaction, J(dd), that is dominant in the system. Quite unusual crossover from a three-dimensional ordering to a one-dimensional magnet occurs when magnetic fields are applied parallel to the a axis. A notable anisotropic field-direction dependence against the in-plane magnetic field was also observed in the transition temperature of the bulk superconductivity by the angle-resolved heat capacity measurements. We discuss the origin of this in-plane anisotropy in terms of the 3d electron spin configuration change induced by magnetic fields.
• Site-specific C-13 NMR study on the locally distorted triangular lattice of the organic conductor k-(BEDT-TTF)(2)Cu-2(CN)(3)

  Saito Y, Minamidate T, Kawamoto A, Matsunaga N, Nomura K

  PHYSICAL REVIEW B 98 20 2018年11月21日 [査読有り][通常論文]
  
• Density Wave State in New alpha-Type Organic Conductor, alpha-(BEDT-TTF)(2)MHg(XCN)(4) (M = NH4, X = Se): A Key Material for Universal Phase Diagram of X = S and X = Se Systems

  Ohnuma Akihiro, Taniguchi Hiromi, Takahashi Yukihiro, Kawamoto Atsushi

  JOURNAL OF PHYSICAL CHEMISTRY C 122 42 24321 - 24328 American Chemical Society ({ACS}) 2018年10月25日 [査読有り][通常論文]
   

  A family of organic conductors, alpha-(BEDT-TTF)(2)MHg(SCN)(4), is known to show the density wave (DW) state for M = Tl, K, and Rb salts, or the superconducting (SC) state for M = NH4 salt at low temperatures. In contrast, alpha-(BEDT-TTF)(2)MHg(SeCN)(4) shows no phase transition and retains its metallic characteristics down to low temperatures. Since no alpha-(BEDTTTF)(2)MHg(SeCN)(4) salt shows the DW or SC states, it was unclear whether the system of alpha-(BEDT-TTF)(2)MHg(SeCN)(4) could be understood by the same phase diagram as that of alpha-(BEDT-TTF)(2)MHg(SCN)(4). Here, we succeeded in synthesizing a key material, alpha-(BEDT-TTF)(2)NH4Hg(SeCN)(4), and determined its crystal structure. The temperature dependence of its electric conductivity and spin susceptibility showed its DW state at low temperatures, indicating that the alpha-(BEDT-TTF)(2)MHg(SeCN)(4) system is linked to the alpha-(BEDTTTF)(2)MHg(SCN)(4) system. From the established phase diagram, we found that the dihedral angle between crystallographically independent A and B molecules, Theta(B), and that between A and C molecules, Theta(C), are good tuning parameters as in theta-type BEDT-TTF salts. In the Theta(B)-Theta(C) plot, the SC salt is located in the large Theta(B) and small Theta(C) regions, whereas the metallic salts are located in the small Theta(B) and large Theta(C) regions. The DW salts are located in the intermediate Theta(B) and Theta(C) regions. The relationship between their location in the Theta(B)-Theta(C) plot and the ground states supports the prediction that the local density of state between A and B molecules determines the ground states.
• Multistep Development of the Hyperfine Fields in lambda-(BEDT-STF)(2)FeCl4 Studied by Mossbauer Spectroscopy

  Fukuoka Shuhei, Sawada Masashi, Minamidate Takaaki, Matsunaga Noriaki, Nomura Kazushige, Ihara Yoshihiko, Kawamoto Atsushi, Doi Yoshihiro, Wakeshima Makoto, Hinatsu Yukio

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 87 9 2018年09月15日 [査読有り][通常論文]
   

  We have investigated the magnetic properties of lambda-(BEDT-STF)(2) FeCl4 by Mossbauer measurement to reveal the origin of the paramagnetic-like behavior of the 3d spin system observed in lambda-(BEDT-STF)(2) FeCl(4 )using the donor substitution effect. We found that the temperature dependence of the hyperfine fields shows multistep development below T-N of 16K. From comparison of the Mossbauer results and a theoretical model, we demonstrated that the multistep development is caused by coupling between the 3d spins and the pi spins with strong spin correlation. We propose that the multistep development of the hyperfine fields is an intrinsic behavior induced by the pi-d interaction.
• Role of the d-d interaction in the antiferromagnetic phase of λ-(BEDT-STF)2FeCl4

  Takaaki Minamidate, Hironori Shindo, Yoshihiko Ihara, Atsushi Kawamoto, Noriaki Matsunaga, Kazushige Nomura

  Physical Review B 97 10 2018年03月05日 [査読有り][通常論文]
   

  Magnetic susceptibility and proton nuclear magnetic resonance (H1-NMR) measurements were performed for the quasi-two-dimensional π-d interacting system λ-(BEDT-STF)2FeCl4 at ambient pressure. Magnetic susceptibility arising from the 3d spins of the FeCl4 anion show an anisotropy at low temperature and its temperature dependence for the external field parallel to the c axis is described as a broad peak structure at 8 K. A sharp peak in the temperature dependence of T1-1 associated with the antiferromagnetic (AF) transition is observed at TAF=16 K, together with the drastic splitting of the NMR spectrum below TAF. The relation between the static susceptibility and the splitting of the NMR shift suggests the existence of the relatively strong d-d AF interaction. These results can be explained by the model considering the AF-coupled d-spin system in the AF long-range-ordered π-spin system. We find that the AF phases in λ-type salts can be universally explained by this model.
• Coupling of molecular motion and electronic state in the organic molecular dimer Mott insulator β′ -(BEDT-TTF) 2ICl2

  Masashi Sawada, Shuhei Fukuoka, Atsushi Kawamoto

  Physical Review B 97 4 2018年01月19日 [査読有り][通常論文]
   

  We have performed H1 NMR and C13 NMR measurements to investigate the coupling between molecular dynamics and the electronic state of β′-(BEDT-TTF)2ICl2. From the H1 NMR measurements, we observed a frequency-dependent anomaly in the nuclear spin-lattice relaxation rate T1-11 that originates from the slowing down of the ethylene motion. In the C13 NMR measurements, we found an anomaly in the linewidth of the NMR spectra at around 150 K, which is attributed to a nuclear spin-spin relaxation rate (T213) anomaly. The magnitudes of the anomalies in the linewidth and in T2-113 are related to the hyperfine coupling constant. These results suggest that the ethylene motion modulates the molecular orbital of the BEDT-TTF molecules and gives rise to a difference in the orbital energy between the "staggered" and "eclipsed" conformations. We propose that significant coupling exists between the ethylene motion and the electronic state of the molecular dimer and that the ethylene dynamics can trigger the emergence of charge degrees of freedom inside the dimers and cause the dielectric anomaly in β′-(BEDT-TTF)2ICl2.
• 有機超伝導体λ-(BETS)₂GaCl₄の⁶⁹Ga-NMRによる研究

  辻 晃平, 小林 拓矢, 河本 充司

  日本物理学会講演概要集 73 0 1770 - 1770 一般社団法人 日本物理学会 2018年
• Antiferromagnetic ordering in organic conductor λ-(BEDT-TTF)2GaCl4 probed by 13CNMR

  Yohei Saito, Shuhei Fukuoka, Takuya Kobayashi, Atsushi Kawamoto, Hatsumi Mori

  Journal of the Physical Society of Japan 87 1 2018年 [査読有り][通常論文]
   

  The ground state of λ-(BEDT-TTF)2GaCl4, which has the same structure as the organic superconductor λ-(BETS)2-GaCl4, was investigated by magnetic susceptibility and 13C NMR measurements. The temperature dependence of the magnetic susceptibility revealed an antiferromagnetic (AF) correlation with J/kB ∼ 98 K. NMR spectrum splitting and the divergence of 1=T1 were observed at approximately 13 K, which is associated with the AF transition. We found that the AF structure is commensurate according to discrete NMR peak splitting, suggesting that the ground state of λ- (BEDT-TTF)2GaCl4 is an AF dimer-Mott insulating state. Our results suggest that the superconducting phase of λ-type salts would be located near the AF insulating phase.
• Evidence of antiferromagnetic fluctuation in the unconventional superconductor lambda-(BETS)(2)GaCl4 by C-13 NMR

  T. Kobayashi, A. Kawamoto

  PHYSICAL REVIEW B 96 12 2017年09月 [査読有り][通常論文]
   

  We performed C-13 NMR measurements on the unconventional organic superconductor lambda-(BETS)(2)GaCl4 to clarify its electronic properties in the paramagnetic state. We found that the spin-lattice relaxation rate divided by temperature 1/T1T shows Curie-like enhancement above 55 K that arises from an antiferromagnetic fluctuation. In addition, we found additional enhancement of 1/T1T below 10 K, where the Knight shift decreases and the linewidth of NMR spectra is broadened. The result could be understood by the magnetic fluctuation induced by the nesting of the Fermi surface. We discovered that lambda-(BETS)(2)GaCl4 salt inherently exhibits the two different types of magnetic fluctuations.
• κ-(ET)₂Cu[N(CN)₂]Iにおける圧力下¹³C NMR測定

  鈴田 耀大, 小林 拓矢, 井原 慶彦, 河本 充司

  日本物理学会講演概要集 72 0 1849 - 1849 一般社団法人 日本物理学会 2017年 

  有機伝導体!LaTeX$\kappa$-(ET)_2_Cu[N(CN)_2_]X (X=Br,Cl)は盛んに研究されており、同一の温度-圧力相図で理解される。X=Cl,Br塩と同形であるX=I塩もイオン半径の類推から金属相に位置すると考えられるが、電気抵抗測定からは常圧下で絶縁体、圧力下で超伝導体であることがわかっている。X=I塩の物性が共通の温度-圧力相図で理解できないことを明らかにするために常圧及び圧力下における^13^C NMR測定を行った。

• 有機超伝導体λ-(BETS)₂GaCl₄のFFLO状態に関する熱的研究

  今城 周作, 山下 智史, 圷 広樹, 熊谷 浩也, 小林 拓矢, 河本 充司, 中澤 康浩

  日本物理学会講演概要集 72 0 1864 - 1864 一般社団法人 日本物理学会 2017年 

  表題物質は特殊な超伝導状態であるFFLO状態を示す候補物質のひとつである。FFLO状態は高い磁場下でゼーマン分裂によるエネルギーの損をクーパー対が重心運動量を持つことで抑えることで発現する超伝導である。本研究では表題物質の高磁場下熱容量測定からFFLO状態の熱力学的な性質を議論する予定である。

• ¹³C-NMR法によるλ-(BETS)₂GaCl₄の反強磁性揺らぎの研究

  小林 拓矢, 河本 充司

  日本物理学会講演概要集 72 0 1865 - 1865 一般社団法人 日本物理学会 2017年 

  !LaTeX$\lambda$-(BETS)_2_GaCl_4_はFFLO超伝導相やd波の超伝導対称性が報告されている非従来型の超伝導体である。超伝導メカニズムを解明するためには、まず超伝導転移温度以上における常伝導相の電子状態を調べることが必要である。しかしこれまでのところ、それを明らかにする適切なプローブがなかった。本研究では、BETS分子の中心の炭素を^13^Cに置換した試料を作製し、^13^C NMR測定を行った。その結果、およそ90K以上に反強磁性ゆらぎがあることを発見した。

• ¹³C‒NMR法によるλ-(BETS)₂GaCl₄の超伝導ギャップ対称性の研究

  小林 拓矢, 井原 慶彦, 河本 充司

  日本物理学会講演概要集 72 0 1518 - 1518 一般社団法人 日本物理学会 2017年
• Static and dynamic interaction between pi and d electrons in organic superconductor beta ''-(BEDT-TTF)(4)[(H3O)Fe(C2O4)(3)] center dot C6H5Br studied by C-13 NMR spectroscopy

  Y. Ihara, Y. Futami, A. Kawamoto, K. Matsui, T. Goto, T. Sasaki, S. Benmansour, C. J. Gomez-Garcia

  PHYSICAL REVIEW B 94 6 2016年08月 [査読有り][通常論文]
   

  We present the results of C-13 NMR experiments in an organic superconductor with localized Fe spins beta ''-(BEDT-TTF)(4)[(H3O)Fe(C2O4)(3)] center dot C6H5Br. We reveal the antiferromagnetic coupling between Fe d spins and pi spins, which creates an exchange field antiparallel to the external field direction at the pi electrons. In addition to the static effects of Fe spins, we show from the nuclear spin-lattice relaxation rate measurement that the magnetic fluctuations generated by Fe spins are suppressed at low temperatures and high magnetic fields. These conditions are suitable to stabilize the field-induced superconductivity by the field compensation mechanism. After the suppression of Fe-spin dynamics by a magnetic field of 19 T, we observed the underlying pi-electron contribution. We discuss a possible anomaly in the pi-electron system.
• Thermodynamic Evidence of d-Wave Superconductivity of the Organic Superconductor lambda-( BETS)(2)GaCl4

  Shusaku Imajo, Naoki Kanda, Satoshi Yamashita, Hiroki Akutsu, Yasuhiro Nakazawa, Hiroya Kumagai, Takuya Kobayashi, Atsushi Kawamoto

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 85 4 2016年04月 [査読有り][通常論文]
   

  Low-temperature heat capacity of the organic superconductor lambda-(BETS)(2)GaCl4 in a temperature range between 0.6 and 10K was measured for a single crystal sample by relaxation calorimetry technique. The contribution of electronic heat capacity in the superconducting state shows T-2 dependence at lower temperature that indicates the existence of quasi-particle excitations from the line-nodal gap structure of d-wave pairing. The recovery of the electronic heat capacity coefficient, gamma by magnetic field shows H-1/2 dependence that is consistent with the picture of line-nodal superconductor. In spite of the different packing from typical organic superconductors kappa-(BEDT-TTF)(2)X, the lambda-type BETS salt also shows a feature of d-wave symmetry pairing.
• Modification of local electronic state by BEDT-STF doping to kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br salt studied by C-13 NMR spectroscopy

  T. Kobayashi, Y. Ihara, A. Kawamoto

  PHYSICAL REVIEW B 93 9 2016年03月 [査読有り][通常論文]
   

  We present the results of site-selective C-13 NMR spectroscopy on an organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br(kappa-Br) doped with BEDT-STF molecules. We reveal microscopically the modulation of the local electronic state caused by the BEDT-STF doping from the C-13 NMR measurement on two types of samples, which are C-13 enriched kappa-Br doped with naturally abundant BEDT-STF molecules, and natural kappa-Br doped with C-13 enriched BEDT-STF molecules. The results of the nuclear spin-lattice relaxation rate 1/T-1 measured both in the normal and superconducting state suggest that the potential disorder at the BEDT-STF sites scatters antiferromagnetic interaction and superconducting Cooper pairs.
• Determination of the hyperfine coupling tensor in organic conductors kappa-(BEDT-TTF)(2)X (X=Cu[N(CN)(2)]Br, Cu(NCS)(2)) on central C-13 sites

  Y. Saito, A. Kawamoto

  SOLID STATE NUCLEAR MAGNETIC RESONANCE 73 22 - 30 2016年02月 [査読有り][通常論文]
   

  Although the organic superconductors kappa-(BEDT-TTF)(2X) (X=Cu[N(CN)(2)]Br and Cu(NCS)(2)) have been studied by NMR spectroscopy, hyperfine coupling tensors are required to quantify NMR spectra. Angle dependences of NMR spectra were measured to determine hyperfine coupling tensors applicable to further NMR assessments of attractive physical phenomena on kappa-salts. The tensors of kappa-(BEDT-TTF)(2X) and beta' -(BEDT-TTF)(2)ICl2 salts were compared to determine the hyperfine coupling mechanism in organic metals, with the results indicating that off-site dimer contribution should be considered. We also report the electron correlation of these salts and further application of the tensors. (C) 2015 Elsevier Inc. All rights reserved.
• 22pBE-4 π-d系有機導体λ-(BEDT-STF)_2FeCl_4の磁気的性質

  南舘 孝亮, 進藤 寛礼, 松永 悟明, 野村 一成, 井原 慶彦, 河本 充司

  日本物理学会講演概要集 71 1953 - 1953 一般社団法人日本物理学会 2016年
• 19pAR-9 有機超伝導体β''-(BEDT-TTF)_4Pt(CN)_4・H_2Oの電荷秩序相のNMR研究

  藁谷 拓実, 二見 洋輔, 井原 慶彦, 河本 充司

  日本物理学会講演概要集 71 1841 - 1841 一般社団法人日本物理学会 2016年
• 19pAR-8 圧力下NMR実験によるβ''-(BEDT-TTF)_4[(H_3O)Ga(C_2O_4)_3]・C_6H_5NO_2の電荷秩序状態と超伝導状態の研究

  井原 慶彦, 二見 洋輔, 河本 充司

  日本物理学会講演概要集 71 1840 - 1840 一般社団法人日本物理学会 2016年
• 有機超伝導体β-(BEDT-TTF)₂I₃の圧力下における¹³C-NMR測定

  熊谷 浩也, 斉藤 洋平, 井原 慶彦, 河本 充司

  日本物理学会講演概要集 71 1677 - 1677 一般社団法人 日本物理学会 2016年 

  超高圧下で超伝導を示す\beta^{\prime}-(BEDT-TTF)_2_ICl_2_の超伝導モデル物質として\beta-(BEDT-TTF)_2_I_3_がある。\beta-(BEDT-TTF)_2_I_3_はその圧力状態や冷却方法により二つの超伝導転移温度を持つことが知られている有機超伝導物質である。その超伝導の起源を探るため、圧力下でのNMR測定を行うことで、スピン-格子緩和時間T_1_やKight shift、電子相関の情報を得る一つの指標となるKorringa因子等の圧力依存性を調べ、超伝導との関連性が指摘されている磁気的な揺らぎについて議論した。

• ESR分光法によるb''-(BEDT-TTF)₄[(H₃O)Fe(C₂O₄)₃]C6H5Brのスピン相関の研究

  井原 慶彦, 二見 洋輔, 河本 充司, Benmansour Samia, Gomez-Garcia Carlos J.

  日本物理学会講演概要集 71 1681 - 1681 一般社団法人 日本物理学会 2016年 

  有機超伝導体b''-(BEDT-TTF)_4_[(H_3_O)Fe(C_2_O_4_)_3_]C6H5Brは磁場中でp電子にかかる外部磁場を局在Feスピンと遍歴p電子の間の交換相互作用がちょうど打ち消し、有効的にゼロ磁場を作り出すことで発現する磁場誘起超伝導の可能性が議論されている。今回スピン相関を直接的に観測出来るESR分光法によりpスピンとFeスピンの間の相互作用を調べたので、その結果を報告する。

• λ-(BETS)₂GaCl₄の超伝導ギャップ構造

  今城 周作, 管田 尚輝, 山下 智史, 圷 広樹, 熊谷 浩也, 小林 拓矢, 河本 充司, 中澤 康浩

  日本物理学会講演概要集 71 1686 - 1686 一般社団法人 日本物理学会 2016年 

  有機超伝導体の一つλ-(BETS)_2_GaCl_4_はDimer Mott系の塩であると考えられ、そのため反強磁性スピンゆらぎを起源としたd波超伝導が発現している可能性が考えられている。そこで熱容量測定から超伝導状態の準粒子の低エネルギー励起構造からギャップ構造の研究を行い、d波超伝導状態であることを決定した。

• (TMTTF)₂Xのスピン密度波相における非線形電気伝導II

  千葉 大祐, 松永 悟明, 野村 一成, 河本 充司

  日本物理学会講演概要集 71 1709 - 1709 一般社団法人 日本物理学会 2016年 

  擬一次元導体である(TMTTF)_2_PF_6_は、2.0GPa以上の圧力下で不整合スピン密度波を基底状態にも持つ。我々はこれまで(TMTTF)_2_PF_6_において、しきい電場を大きく上まわる電場を印可した際に、電流密度の上昇に対し電場が減少していく負性微分抵抗を観測している。今回、この負性微分抵抗の起源を解明するために、(TMTTF)_2_PF_6_でさらに高電場領域でのI-V特性を調べ、負性微分抵抗とSDWスライディングとの関係について報告・議論する。

• 一軸圧下NMR実験によるα-(BEDT-TTF)₂RbHg(SCN)₄の電荷密度波相と超伝導相の研究

  大沼 晃浩, 熊谷 浩也, 藁谷 拓実, 小林 拓矢, 斎藤 洋平, 福岡 脩平, 井原 慶彦, 河本 充司

  日本物理学会講演概要集 71 1675 - 1675 一般社団法人 日本物理学会 2016年 

  電荷密度波相近傍に超伝導が見つかっている物質として\alpha-(BEDT-TF)_2_MHg(SCN)_4_ (M=K，Rb，NH_4_)がある。Rb塩はT_CDW_=12 Kで電荷密度波転移し、NH_4_塩はT_C_=1.5 Kで超伝導転移する。二つの塩の関係は一軸圧法で調べられており、c軸圧により超伝導が誘起されることが示唆されている。超伝導の誘起に伴う電子状態の変化を観測するために、Rb塩を対象にc軸圧下NMR測定を行った。

• π-d系有機導体λ'-(BEDT-STF)₂FeBr₄の磁気的性質

  和田 大阿, 南館 孝亮, 松永 悟明, 野村 一成, 河本 充司

  日本物理学会講演概要集 71 1589 - 1589 一般社団法人 日本物理学会 2016年 

  !LaTeX${\lambda}$-(BETS)_2_FeCl_4_において!LaTeX${\pi}$電子とd電子の相互作用による反強磁性秩序形成の可能性が示唆され、この秩序の起源については議論がなされている。この度我々は新たな!LaTeX${\pi -d}$系物質として、!LaTeX${\lambda^{\prime } }$-(BEDT-STF)_2_FeBr_4_の結晶を作成し、その物性を測定した。講演ではこの物質の磁気的性質と高圧力下における電気抵抗の振る舞い、!LaTeX${\lambda^{\prime } }$-(BEDT-STF)_2_FeBr_4_の反強磁性秩序の起源について示す。

• High-Temperature Charge and Structure Anomalies in beta"-(BEDT-TTF)(4)[(H3O)Ga(C2O4)(3)]center dot C6H5NO2

  Yoshihiko Ihara, Yosuke Futami, Atsushi Kawamoto

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 85 1 2016年01月 [査読有り][通常論文]
   

  We have performed specific heat, X-ray diffraction, electron spin resonance (ESR), and NMR experiments on the organic superconductor beta"-(BEDT-TTF)(4)[(H3O)Ga(C2O4)(3)]center dot C6H5NO2 (beta"-Ga) salt at high temperatures to reveal the origin of the resistivity minimum observed around 100 K. Since splitting of the Raman spectrum was observed at a charge-sensitive vibration mode, the anomaly around 100 K has been ascribed to a charge instability with fractional charge imbalance. In addition, another charge instability was detected at 8.5 K in a previous NMR experiment. The origin of these anomalies observed at different temperatures should be investigated to uncover the electronic state in which superconductivity occurs. Our results suggest that the beta"-Ga salt undergoes a thermodynamic charge transition at T-CO = 90 K, which has a different origin from the charge instability observed at 8.5 K in the NMR experiment. We discuss the possible connection between these charge instabilities by comparing the present results with those obtained for other BEDT-TTF salts with two charge-ordering transitions.
• Charge Order in (TMTTF)(2)TaF6 by Infrared Spectroscopy

  Yuki Oka, Noriaki Matsunaga, Kazushige Nomura, Atsuhi Kawamoto, Kaoru Yamamoto, Kyuya Yakushi

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 11 2015年11月 [査読有り][通常論文]
   

  We have performed infrared spectroscopy in (TMTTF)(2)TaF6 (TMTTF: tetramethyltetrathiafulvalene) to investigate the relationship between the charge order (CO) state and the antiferromagnetic (AF) insulating ground state. A clear peak splitting corresponding to the charge disproportionation was observed below the CO transition temperature. We estimated the degree of charge disproportionation, Delta rho = rho(rich) - rho(poor), as 0.28e from the peak splitting and found that the CO state coexists with the AF state and there is no charge redistribution below the AF transition.
• Raman Spectroscopy Study of Charge Fluctuation in the Spin-Liquid Candidate kappa-(BEDT- TTF)(2)Cu-2(CN)(3)

  Kyuya Yakushi, Kaoru Yamamoto, Takashi Yamamoto, Yohei Saito, Atsushi Kawamoto

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 8 2015年08月 [査読有り][通常論文]
   

  We present experimental evidence for the charge fluctuation in the spin-liquid candidate kappa-(BEDT-TTF)(2)Cu-2(CN)(3). The temperature and pressure dependence of the Raman spectrum in the region of 1300-1600 cm(-1) were measured. The charge-sensitive v(2) mode at 1500 cm(-1) exhibited a linewidth broadening below 60K when the sample was slowly cooled. This broadening is induced by a structural change (increase in interdimer transfer integrals). The hydrostatic pressure significantly suppressed the broadening in the metallic phase. This result indicates that the linewidth broadening originates from the valence (charge) fluctuation within the BEDT-TTF dimer, because the screening effect suppresses the interdimer Coulomb interaction that causes the charge disproportionation. The line shape was analyzed using the fast fluctuating model and slow or static inhomogeneous model.
• Tunneling Spectroscopy in Organic Superconductor kappa-(BEDT-TTF-d[3,3])(2)Cu[N(CN)(2)]Br

  Yuki Oka, Hiroyoshi Nobukane, Noriaki Matsunaga, Kazushige Nomura, Kazuhiro Katono, Koichi Ichimura, Atsushi Kawamoto

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 6 2015年06月 [査読有り][通常論文]
   

  We performed tunneling spectroscopy (STS) measurement in an organic superconductor, partially deuterated kappa(BEDT-TTF-d[3,3])(2)Cu[N(CN)(2)]Br. We carried out angle-resolved STS on cut lateral surfaces by the focused ion beam (FIB) method as well as as-grown single-crystal surfaces. It was found that the d[3,3]-Br salt is a strong-coupling d-wave superconductor and that the nodal direction is at an angle of pi/4 from the a*-axis, corresponding to the d(x)(-y)(2)(2) symmetry in the bulk superconducting phase. It is understood that the electron correlation in the d[3,3]-Br salt is not strong enough on the basis of the spin fluctuation mechanism. On the other hand, we also observed two types of superconducting gap. This suggests the coexistence of the d(x)(-y)(2)(2) and d(xy) symmetries. This indicates a change in the symmetry from d(x)(-y)(2)(2) in the bulk superconducting phase to d(xy) around the insulating region with increasing electron correlation.
• Superconducting Phase in lambda-(BEDT-STF)(2)GaCl4 at High Pressures

  Takaaki Minamidate, Yuki Oka, Hironori Shindo, Toshitaka Yamazaki, Noriaki Matsunaga, Kazushige Nomura, Atsushi Kawamoto

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 6 2015年06月 [査読有り][通常論文]
   

  Electrical resistivity measurements under pressure were conducted on the organic conductor lambda-(BEDT-STF)(2)GaCl4, which is situated between lambda-(ET)(2)GaCl4 and lambda-(BETS)(2)GaCl4. Magnetic susceptibility was also measured at ambient pressure. A drop in resistivity, which is associated with the superconducting transition, was observed at T-c approximate to 5K above 1.22 GPa. The superconducting phase was confirmed by pair-breaking under a magnetic field. This is the first observation of superconductivity in lambda-(BEDT-STF)(2)GaCl4. The temperature dependence of spin susceptibility suggests a two-dimensional antiferromagnetic spin system without any magnetic ordering. The phase adjacent to the superconducting phase in lambda-type systems is not the antiferromagnetic phase, unlike the case for kappa-(ET)(2)X.
• Coexistence of charge order and antiferromagnetism in (TMTTF)(2)SbF6: NMR study

  K. Nomura, M. Yamamoto, N. Matsunaga, S. Hirose, N. Shimohara, T. Satoh, T. Isome, Y. Liu, A. Kawamoto

  PHYSICA B-CONDENSED MATTER 460 53 - 57 2015年03月 [査読有り][通常論文]
   

  The electronic state of (TMTTF)(2)SbF6 was investigated by the H-1 and C-13 NMR measurements. The temperature dependence of T-1(-1) in H-1 NMR shows a sharp peak associated with the antiferromagnetic transition at T-AF = 6 K. The temperature dependence of T-1(-1) is described by the power law T-2.4 below T-A. This suggests the nodal gapless spin wave excitation in antiferromagnetic phase. In 13C NMR, two sharp peaks at high temperature region, associated with the inner and the outer carbon sites in TMTTF dimer, split into four peaks below 150 K. It indicates that the charge disproportionation occurs. The degree of charge disproportionation Delta rho is estimated as (025 +/- 0.09)e from the chemical shift difference. This value Delta rho is consistent with that obtained from the infrared spectroscopy. In the antiferromagnetic state (AFI), the observed line shape is well fitted by eight Lorentzian peaks. This suggests that the charge order with the same degree still remains in the AF state. From the line assignment, the AF staggered spin amplitude is obtained as 0.70 mu(B) and 0.24 mu(B) at the charge rich and the poor sites, respectively. These values corresponding to almost 1 mu(B) per (timer are quite different from 0.11 mu(B) of another AF (AFII) state in (TMITF)(2)Br with effective higher pressure. As a result, it is understood that the antiferromagnetic staggered spin order is stabilized on the CO state in the AFI phase of (TMTTF)2(S)bF(6). (C) 2014 Elsevier B.V. All rights reserved
• STM spectroscopy on deuterated kappa-(ET-d[3,3])(2)Cu[N(Cn)(2)]Br

  Y. Oka, H. Nobukane, N. Matsunaga, K. Nomura, K. Katono, K. Ichimura, A. Kawamoto

  PHYSICA B-CONDENSED MATTER 460 93 - 95 2015年03月 [査読有り][通常論文]
   

  We performed the STM Spectroscopy (STS) measurement on organic superconductor deuterated kappa-(ET-d[3,3])(2)Cu[N(CN)(2)]Br to clarify the mechanism of superconductivity. The mechanism of superconductivity in kappa-ET2X is predicted as the spin fluctuation mechanism where the gap symmetry changes from d(x2-y2) to d(xy) with increasing the electron correlation. In previous STS measurements, we found that d[2,2]-Br, d[0,0]-Br and Cu(NCS)(2) were d-wave superconductors and the symmetry was described by the d(x2-y2). The electron correlation of these salts is still weak in the frame of the spin fluctuation model. So, we investigated the d[3,3]-Br which located at stronger electron correlation region than the previously studied salts by the STS. We also investigated the STS on the cut lateral surfaces by the focused ion beam (FIB) method to measure the in-plane anisotropy of superconducting gap in more detail as well as the asgrown surfaces, It was found from the result that d[3,3]-Br was d-wave superconductor and the gap symmetry was d(x2-y2) as well as the previously studied ET salts. Therefore, d[3,3]-Br is also still weak in spite of stronger electron correlation than other ET salts. On the other hand, we also observed the two-type superconducting gaps which are the nodal and anti-nodal type gaps at the same angle surface. This suggests the coexistence of d(x2-y2) and d(xy). It may be the evidence of the change from d(x2-y2) to d(xy) caused by the locally stronger electron correlation around the anti-ferromagnetic insulating region. (C) 2014 Elsevier B.V. All rights reserved.
• 17pAF-8 有機超伝導体β-(BEDT-TTF)_2I_3の常圧下における超微細結合テンソルの決定

  熊谷 浩也, 斎藤 洋平, 河本 充司

  日本物理学会講演概要集 70 1578 - 1578 一般社団法人日本物理学会 2015年
• 18pAH-2 有機超伝導体β"-(BEDT-TTF)_4[(H_3O)Ga(C_2O_4)_3]^-C_6H_5NO_2の静水圧下超伝導状態

  井原 慶彦, 二見 洋輔, 河本 充司

  日本物理学会講演概要集 70 1630 - 1630 一般社団法人日本物理学会 2015年
• 17pAF-1 (TMTTF)_2Xのスピン密度波相における非線形電気伝導

  千葉 大祐, 山浦 大輔, 松永 悟明, 野村 一成, 河本 充司

  日本物理学会講演概要集 70 1572 - 1572 一般社団法人日本物理学会 2015年
• 23pAC-15 λ-(BEDT-STF)_2GaCl_4の^1H-NMR

  進藤 寛礼, 岡 雄基, 山崎 俊隆, 松永 悟明, 野村 一成, 河本 充司

  日本物理学会講演概要集 70 1878 - 1878 一般社団法人日本物理学会 2015年
• 22aAS-11 β"-(BEDT-TTF)_4[(H_3O)Fe(C_2O_4)_3]-C_6H_5Brの高磁場NMR実験によるスピン状態の研究

  二見 洋輔, 井原 義彦, 河本 充司, Gomez-Garcia Carlos J.

  日本物理学会講演概要集 70 1843 - 1843 一般社団法人日本物理学会 2015年
• 23pAC-14 λ-(BEDT-STF)_2GaCl_4の高圧力下超伝導

  南舘 孝亮, 岡 雄基, 山崎 敏隆, 松永 悟明, 野村 一成, 河本 充司

  日本物理学会講演概要集 70 1877 - 1877 一般社団法人日本物理学会 2015年
• 21aAS-2 片側^<13>C置換(TMTTF)_2Brの^<13>C-NMRによる低温AF相の研究

  居初 知征, 井原 義彦, 河本 充司

  日本物理学会講演概要集 70 1785 - 1785 一般社団法人日本物理学会 2015年
• 24aAB-7 α'-(BEDT-TTF)_2IBr_2の電荷秩序相における誘電特性

  野口 郁乃, 松永 悟明, 野村 一成, 河本 充司

  日本物理学会講演概要集 70 1885 - 1885 一般社団法人日本物理学会 2015年
• C-13 NMR study of the charge-ordered state near the superconducting transition in the organic superconductor ss"-(BEDT-TTF)(4)[(H3O)Ga(C2O4)(3)]center dot C6H5NO2

  Y. Ihara, M. Jeong, H. Mayaffre, C. Berthier, M. Horvatic, H. Seki, A. Kawamoto

  PHYSICAL REVIEW B 90 12 2014年09月 [査読有り][通常論文]
   

  The charge-ordered state in a quasi-two-dimensional organic superconductor ss"-(BEDT-TTF)(4)[(H3O)Ga(C2O4) 3]center dot C6H5NO2 has been investigated using C-13 NMR spectroscopy in a high magnetic field. Enhanced resolution of the high-field spectrum allows us to estimate the site charges in the low-temperature charge-ordered state below 8.5 K. The observed strong increase in the charge imbalance suggests that superconductivity appears on the electronic state with a strong charge modulation. From the NMR intensity ratio of signals from the charge-rich and charge-poor sites, we discuss a possible charge pattern with threefold modulation, which could be stabilized by the effects of electron-electron correlations.
• Molecular motion and high-temperature paramagnetic phase in kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl

  Miko Matsumoto, Yohei Saito, Atsushi Kawamoto

  PHYSICAL REVIEW B 90 11 2014年09月 [査読有り][通常論文]
   

  The organic conductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl has been studied for the examination of the conducting mechanism of the semiconducting behavior at high temperatures by C-13-NMR spectroscopy. We found that the temperature dependence of the linewidths and the spin-spin relaxation rate T-2(-1) showed a peak structure characterized by the hyperfine coupling constant in this region, suggesting a connection between ethylene motion and conducting electrons similar to that observed in kappa-(BEDT-TTF)(2)Cu(NCS)(2). Although kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl salt was thought to be an insulator at high temperature, our findings suggest that all kappa-type salts at high temperatures could be in the same phase where the scattering caused by ethylene motion is added to bad metal.
• Microscopic modulation of local density of states in superconducting alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4) studied by site-selective C-13-NMR spectroscopy

  Y. Ihara, K. Noda, A. Kawamoto

  PHYSICAL REVIEW B 90 4 2014年07月 [査読有り][通常論文]
   

  The local electronic state at every crystallographically independent molecular site was separately investigated in the organic superconductor alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4) using site-selective C-13-NMR spectroscopy. The density of states (DOS) at three molecular sites shows independent temperature variation, which is caused by the long-range Coulomb interaction. Comparing the present results with those for a nonsuperconducting counterpart alpha-(BEDT-TTF)(2)RbHg(SCN)(4), we found that the uniform DOS at two of three independent molecular sites is crucial to induce superconductivity. Taking the site-dependent DOS as a parameter, we constructed a phase diagram for a superconductor with long-range Coulomb interaction, an alpha-type BEDT-TTF family, and summarized the competition between charge instability and superconductivity.
• Microscopic observation of superconducting fluctuations in kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br by C-13 NMR spectroscopy

  T. Kobayashi, Y. Ihara, Y. Saito, A. Kawamoto

  PHYSICAL REVIEW B 89 16 2014年04月 [査読有り][通常論文]
   

  We performed C-13-NMR experiment and measured spin-lattice relaxation rate divided by temperature 1/T1T near the superconducting (SC) transition temperature T-c in kappa-(BEDT-TTF)(2)Cu[N(CN)(2)] Br (kappa-Br salt), and kappa-(BEDT-TTF)(2)Cu(NCS)(2) (kappa-NCS salt). We observed the reduction of 1/T1T starting at the temperature higher than T-c in kappa-Br salt. Microscopic observation of the quasiparticle density of states in the fluctuating SC state revealed the effects of short-range Cooper pairs induced in the normal state to the quasiparticle density of states. We also performed systematic measurements in the fields both parallel and perpendicular to the conduction plane in kappa-Br and kappa-NCS salts, and confirmed that the reduction of 1/T1T above T-c is observed only in kappa-Br salt regardless of the external field orientation.
• C-13 NMR study of commensurate antiferromagnetism in (TMTTF)(2)Br

  Shinji Hirose, Yang Liu, Atsushi Kawamoto

  PHYSICAL REVIEW B 88 12 2013年09月 [査読有り][通常論文]
   

  Quasi-one-dimensional organic conductors (TMTCF)(2)X have various electric and magnetic properties. Although theoretical and experimental studies have suggested that (TMTTF)(2)Br has the properties of commensurate antiferromagnetism, details of the magnetic structure of this compound are unclear. Two types of antiferromagnetism are expected, one due to a localized electron and the other to the nesting of the Fermi surface. We therefore assessed the antiferromagnetic structure of (TMTTF)(2)Br using C-13 NMR. Site assignment of the observed antiferromagnetic spectrum confirmed that there were two magnetic molecular sites, with staggered moments and amplitude of 0.11 mu(B)/molecule, as well as nonmagnetic molecular sites. A commensurate structure with antiferromagnetic ordering of (up arrow omicron down arrow omicron) along a one-dimensional chain would be expected as the freezing of antiferromagnetic fluctuations in the charge-ordered phase of the (TMTTF)(2)AsF6 salt. The presence of a nodal site is strongly suggestive of the nesting type antiferromagnetism. The fine structure of the antiferromagnetic spectrum suggests superlattice along the interchain direction. We could not observe line broadening due to the charge order above the antiferromagnetic transition.
• 13C NMR study of superconductivity near charge instability Realized in β''-(BEDT-TTF)4 [(H3O)Ga(C 2O4)3]·C6H5NO 2

  Yoshihiko Ihara, Harumi Seki, Atsushi Kawamoto

  Journal of the Physical Society of Japan 82 8 2013年08月 [査読有り][通常論文]
   

  To investigate the superconducting (SC) state near a charge instability, we performed 13C NMR experiments on the molecular superconductor (BEDT-TTF)4 [(H3O)Ga(C2O4) 3]·C6H5NO2 [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene], in which charge disproportionation was reported from Raman spectroscopy at 100 K. We found an NMR spectral splitting at TCD = 12 K, which is ascribed to the low-temperature charge instability. Measurements of nuclear spin-lattice relaxation time revealed enhanced fluctuations at TCD. We suggest the relationship between the enhanced. © 2013 The Physical Society of Japan.
• Commensurability of the Spin-Density-Wave State of (TMTSF)(2)PF6 Observed by C-13-NMR

  Sanato Nagata, Masaki Misawa, Yoshihiko Ihara, Atsushi Kawamoto

  PHYSICAL REVIEW LETTERS 110 16 2013年04月 [査読有り][通常論文]
   

  A spin-density-wave (SDW) for (TMTSF)(2)PF6 has been reported to appear below T-SDW (similar or equal to 12 K), with a subphase transition at T* (similar or equal to 4 K). To determine the structure of the subphase, we synthesized (TMTSF)(2)PF6, in which one side of the central carbon bond in each TMTSF molecule was replaced by C-13, and utilized this compound in C-13 nuclear magnetic resonance measurements. Below T-SDW, the spectrum became broad and T-1(-1) decreased, in agreement with previous results. Below T*, fine structures emerged in the center of the spectrum and T-1(-1) decreased exponentially. These phenomena were attributed to the emergence of commensurability at T*. DOI: 10.1103/PhysRevLett.110.167001
• Charge ordering and antiferromagnetism in (TMTTF)(2)SbF6

  Noriaki Matsunaga, Shinji Hirose, Naoki Shimohara, Takehito Satoh, Tomoyuki Isome, Masatoshi Yamomoto, Yang Liu, Atsushi Kawamoto, Kazushige Nomura

  PHYSICAL REVIEW B 87 14 2013年04月 [査読有り][通常論文]
   

  Carbon-13 nuclear magnetic resonance (C-13 NMR) measurements have been carried out in the quasi-one-dimensional organic conductor (TMTTF)(2)SbF6, which exhibits charge ordering (CO) transition and antiferromagnetic (AF) transition at 157 K and 6 K at ambient pressure, respectively. We estimated the degree of charge disproportionation, Delta rho = rho(rich) - rho(poor), in the CO state to be 0.25e from the analysis of the NMR shift and found the broadening of the NMR spectral peaks caused by the inhomogeneous distribution in association with the AF fluctuation at charge rich site below 20 K in the CO state. Moreover, we determined the magnetic structure with two kinds of staggered moments in the AF phase of (TMTTF)(2)SbF6, which suggests that the CO state remains even in the AF phase. Consequently, we found the difference between two AF phases appearing on both sides of the spin-Peierls phase in the universal P-T phase diagram. DOI: 10.1103/PhysRevB.87.144415
• Charge disproportionation with lattice distortion of α-(BEDT-TTF) 2RbHg(SCN)4 observed by 13C-NMR

  Kazuki Noda, Yoshihiko Ihara, Atsushi Kawamoto

  Physical Review B - Condensed Matter and Materials Physics 87 8 2013年02月06日 [査読有り][通常論文]
   

  To explore the connection between α-(BEDT-TTF)2I 3 and α-(BEDT-TTF)2MHg(SCN)4 (M=K, Rb, Tl and NH4) and to resolve the difference between band picture and charge fluctuation of α-(BEDT-TTF)2MHg(SCN)4, we utilized 13C-NMR to examine α-(BEDT-TTF)2RbHg(SCN)4 under the conditions with a large hyperfine coupling constant at each site. The temperature dependence of site susceptibility showed the development of spin disproportionation as observed in α-(BEDT-TTF)2I3. We found that the linewidth of the A site only increased as temperature decreased from 200 to 100 K, a change associated with the development of lattice modulation. These findings indicate that density-wave modulation occurs during charge disproportionation instability. © 2013 American Physical Society.
• Charge disproportionation with lattice distortion of alpha-(BEDT-TTF)(2)RbHg(SCN)(4) observed by C-13-NMR

  Kazuki Noda, Yoshihiko Ihara, Atsushi Kawamoto

  PHYSICAL REVIEW B 87 8 2013年02月 

  To explore the connection between alpha-(BEDT-TTF)(2)I-3 and alpha-(BEDT-TTF)(2)MHg(SCN)(4) (M = K, Rb, Tl and NH4) and to resolve the difference between band picture and charge fluctuation of alpha-(BEDT-TTF)(2)MHg(SCN)(4), we utilized C-13-NMR to examine alpha-(BEDT-TTF)(2)RbHg(SCN)(4) under the conditions with a large hyperfine coupling constant at each site. The temperature dependence of site susceptibility showed the development of spin disproportionation as observed in alpha-(BEDT-TTF)(2)I-3. We found that the linewidth of the A site only increased as temperature decreased from 200 to 100 K, a change associated with the development of lattice modulation. These findings indicate that density-wave modulation occurs during charge disproportionation instability. DOI: 10.1103/PhysRevB.87.085105
• Effect of X-ray Irradiation on the Organic Superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2) Probed by C-13-NMR

  Miko Matsumoto, Hiroki Kato, Yuki Kuwata, Atsushi Kawamoto, Noriaki Matsunaga, Kazushige Nomura

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 11 2012年11月 [査読有り][通常論文]
   

  kappa-(BEDT-TTF)(2)Cu(NCS)(2) [BEDT-TTF: bis(ethylenedithio) tetrathiafulvalene] has semiconductive properties at high temperatures, but these properties are suppressed by X-ray irradiation. Utilizing C-13-NMR, we assessed the effects of X-ray irradiation. When we compared the spectrum and spin-spin relaxation times, T-2, of irradiated and nonirradiated kappa-(BEDT-TTF)(2)Cu(NCS)(2), we found that defects caused by irradiation reduced the connection between ethylene motion and conduction electrons. Measurements of Knight shift and (T1T)(-1) confirmed that irradiation had no effect on carrier density.
• Magnetic and Electric Properties of Organic Conductors Probed by C-13-NMR Using Selective-Site Substituted Molecules

  Shinji Hirose, Masaki Misawa, Atsushi Kawamoto

  CRYSTALS 2 3 1034 - 1057 2012年09月 [査読有り][通常論文]
   

  Quasi-One and quasi-two dimensional organic conductors consisting of TTF derivatives such as BEDT-TTF (bis-(ethylene-dithio)-tetra-thia-fulvalene) and TMTCF (C = S; TMTTF: tetra-methyl-tetra-thia-fulvalene, C = Se; TMTSF: tetra-methyl-tetra-selena-fulvalene) have been well investigated in condensed matter physics because of interest in the emerging electric and magnetic properties, such as the spin density wave, charge order, superconductivity, anti-ferromagnetism, and so on. To probe the electronic state, nuclear magnetic resonance (NMR) is one of the most powerful tools as the microscopic magnetometer. A number of C-13-NMR studies have been performed of the double-site central C-13=C-13 bond substituted molecules. However, problems with the coupled spin system of C-13=C-13 complicated the interpretation for observations on NMR. Therefore, single-site C-13-enriched molecules are desired. We summarize the problem of Pake doublet and the preparation of the single-site C-13-susbstituted BEDT-TTF and TMTCF molecules. We also demonstrate the superiority of C-13-NMR of the single-site C-13-susbstituted molecule utilizing the hyperfine coupling tensor.
• STM Spectroscopy on deuterated kappa-(BEDT-TTF-d[n,n])(2)Cu[N(CN)(2)]Br

  Yuki Oka, Ryota Abe, Hiroyoshi Nobukane, Noriaki Matsunaga, Kazushige Nomura, Koichi Ichimura, Atsushi Kawamoto

  26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 2012年 [査読有り][通常論文]
   

  We performed the STM spectroscopy measurement on deuterated kappa-(BEDT-TTF-d[n, n])(2)Cu[N(CN)(2)]Br to clarify the relation between the superconducting state and the strength of the electron correlation in organic superconductors BEDT-TTF family. We report the results for d[2,2]-salt and d[3,3]-salt with the stronger electron correlation than d[0,0]-salt. The superconducting gap observed as the differential conductance varied systematically depending on the direction of the lateral surface. From the analysis of angular dependent gap function, we found that the node direction of d-wave in d[2,2] and d[3,3] were along a* +/- c* same as d[0,0]. These directions were supported by the observation of the ZBCP near the node direction. It suggests that the dimerization, corresponding to the electron correlation, in both salts is still weak, although these salts are situated near a Mott boundary. While, the node direction rotates a little toward the c* axis in d[3,3] with larger dimerization.
• Correlation between non-Fermi-liquid behavior and antiferromagnetic fluctuations in (TMTSF)(2)PF6 observed using C-13-NMR spectroscopy

  Yoshitaka Kimura, Masaki Misawa, Atsushi Kawamoto

  PHYSICAL REVIEW B 84 4 2011年07月 [査読有り][通常論文]
   

  In the temperature-pressure phase diagram of the organic superconductor (TMTSF)(2)PF6 (TMTSF: tetramethyltetraselenafulvalene), the superconducting phase and the spin-density-wave (SDW) phase are adjacent to each other. This salt exhibits non-Fermi-liquid (NFL) behavior and superconductivity under pressure. Its superconductive property does not exist at higher pressures where Fermi-liquid (FL) behavior is exhibited. In order to investigate the origin of NFL behavior, systematic C-13-NMR measurement of this salt has been assessed under pressure in a wide temperature range. At low temperatures, (T1T)(-1) increases, and this increase is suppressed by the increasing pressure. These results suggest that applying pressure alters the electron system from the NFL to the FL state, and that antiferromagnetic fluctuations contribute to the origin of NFL behavior. The connection between the emergence of FL behavior and the disappearance of superconductivity suggests that the SDW fluctuation relates to the mechanism of the superconductivity in (TMTSF)(2)PF6.
• C-13-NMR studies of the paramagnetic and charge-ordered states of the organic superconductor beta ''-(BEDT-TTF)(3)Cl-2 center dot 2H(2)O under pressure

  Sanato Nagata, Takashi Ogura, Atsushi Kawamoto, Hiromi Taniguchi

  PHYSICAL REVIEW B 84 3 2011年07月 [査読有り][通常論文]
   

  beta ''-(BEDT-TTF)(3)Cl-2 center dot 2H(2)O [BEDT-TTF: bis-(ethylenedithio)tetrathiafulvalene] is superconductive under pressures, whereas the salt exhibits metal-insulator (MI) transition under ambient pressure. The insulator phase in the salt was examined using the charge density wave (CDW) phase that was obtained from band calculation. The charge-ordered (CO) state was recently proposed as the insulator phase of the salt, and the mechanism of superconductivity intermediated by charge fluctuation was suggested. We accessed C-13-NMR on beta ''-(BEDT-TTF)(3)Cl-2 center dot 2H(2)O at ambient pressure and under pressure up to 1.6 GPa. At ambient pressure, the NMR spectrum changed at approximately 100 K. Three isolated peaks appeared at low temperatures, suggesting that the CO state exists below 100 K, and spin-gap behavior was observed. By analyzing the chemical shift, the charges on the three sites were estimated as similar to+0.4e, similar to+0.6e, and similar to+1.0e. The ratio of peak intensity and unsymmetrical peak position suggest the CO state with some symmetry breaking. When pressure is applied, the splitting of the NMR peaks in the CO state is reduced. The salt finally exhibits superconductivity at 1.6 GPa, spin-gap behavior observed at (T1T)(1) below 1.3 GPa suddenly disappears, whereas the NMR spectrum predicts that charge disproportionation coexists with superconductivity. The suppression of the spin-singlet formation observed in (T1T)(-1) at 1.6 GPa suggests the metallic state with the charge disproportionation and the CO instability with some symmetry breaking.
• Low-frequency dynamics of κ-(BEDT-TTF)2Cu(NCS)2 observed by C13 NMR

  Yuki Kuwata, Megumi Itaya, Atsushi Kawamoto

  Physical Review B - Condensed Matter and Materials Physics 83 14 2011年04月04日 [査読有り][通常論文]
   

  κ-(BEDT-TTF)2Cu(NCS)2 [BEDT-TTF: bis-(ethylenedithio)-tetrathiafulvalene] behaves as a semiconductor at high temperatures, whereas it behaves as a Fermi liquid just above the superconducting transition temperature. To reveal the cause of this behavior, we experimented on κ-(BEDT-TTF)2Cu(NCS)2, in which one side of the central C=C in the BEDT-TTF molecules is substituted with C13 nuclei. We perfomed C13-nuclear magnetic resonance (NMR) spectroscopy on this salt and measured the temperature dependence of its spectral linewidths and its spin-spin relaxation time T2. We found anomalies in its linewidths and T2, which we connected to the ethylene motion within the salt. Compared with the C13-NMR measurements of κ-(BEDT-TTF-d8) 2Cu(NCS)2, we obtained the experimental evidence of the connection between the ethylene motion and the conduction electrons. Considering this connection, we examined the semiconductive behavior of κ-(BEDT-TTF)2Cu(NCS)2 at high temperatures. The contribution of ethylene motion to the electronic state is thought to be a common feature of BEDT-TTF salts. © 2011 American Physical Society.
• Low-frequency dynamics of kappa-(BEDT-TTF)(2)Cu(NCS)(2) observed by C-13 NMR

  Yuki Kuwata, Megumi Itaya, Atsushi Kawamoto

  PHYSICAL REVIEW B 83 14 2011年04月 [査読有り][通常論文]
   

  kappa-(BEDT-TTF)(2)Cu(NCS)(2) [BEDT-TTF: bis-(ethylenedithio)-tetrathiafulvalene] behaves as a semiconductor at high temperatures, whereas it behaves as a Fermi liquid just above the superconducting transition temperature. To reveal the cause of this behavior, we experimented on kappa-(BEDT-TTF)(2)Cu(NCS)(2), in which one side of the central C=C in the BEDT-TTF molecules is substituted with C-13 nuclei. We perfomed C-13-nuclear magnetic resonance (NMR) spectroscopy on this salt and measured the temperature dependence of its spectral linewidths and its spin-spin relaxation time T-2. We found anomalies in its linewidths and T-2, which we connected to the ethylene motion within the salt. Compared with the C-13-NMR measurements of kappa-(BEDT-TTF-d8)(2)Cu(NCS)(2), we obtained the experimental evidence of the connection between the ethylene motion and the conduction electrons. Considering this connection, we examined the semiconductive behavior of kappa-(BEDT-TTF)(2)Cu(NCS)(2) at high temperatures. The contribution of ethylene motion to the electronic state is thought to be a common feature of BEDT-TTF salts.
• Local spin susceptibility in the zero-gap-semiconductor state of alpha-(BEDT-TTF)(2)I-3 probed by C-13 NMR under pressure

  Shinji Hirose, Atsushi Kawamoto

  PHYSICAL REVIEW B 82 11 2010年09月 [査読有り][通常論文]
   

  alpha-(BEDT-TTF)(2)I-3 has a double column structure with three crystallographically independent molecules, A, B, and C, and becomes an insulator below 135 K due to a charge-ordering (CO) transition. The CO state is suppressed under pressure and shows weak temperature dependence of the electrical resistance. The decline of the carrier density is observed over 1.8 GPa, suggesting a zero-gap-semiconductor state under high pressure. The local susceptibility on each site provides important information about the electronic band structure. In our previous work, molecular site B became spin poor and molecular site C became spin rich in the metallic state, suggesting the disproportionation of the local spin density. Therefore, it is worthwhile to investigate the behavior of the electron properties of each molecular site. We accessed the C-13-NMR in this salt at ambient pressure and at 2.1 GPa. The analysis of the local spin susceptibility suggests that the disproportionation of the spin susceptibility at 2.1 GPa is enhanced from that at ambient pressure, and the spin susceptibility vanishes at low temperature at 2.1 GPa. Moreover, from the temperature dependence of T-1(-1), we obtain the relation of T-1(-1) proportional to T-3.1.
• Nonuniform site-charge distribution and fluctuations of charge order in the metallic state of alpha-(BEDT-TTF)(2)I-3

  Yue Yue, Kaoru Yamamoto, Mikio Uruichi, Chikako Nakano, Kyuya Yakushi, Shigeaki Yamada, Toshihiro Hiejima, Atsushi Kawamoto

  PHYSICAL REVIEW B 82 7 2010年08月 [査読有り][通常論文]
   

  We present the site-charge distribution in the charge-ordered and metallic states of alpha-(BEDT-TTF)(2)I-3, based on the assignment of the C=C stretching modes nu(2), nu(3), and nu(27) of alpha-(BEDT-TTF)(2)I-3 with the aid of C-13- and deuterium- substituted compounds. The nonuniform site charges in both the metallic and insulating phases were consistent with those determined by a recent x-ray diffraction study. Comparing the line shapes of the charge-sensitive vibrational modes of alpha-(BEDT-TTF)(2)I-3 with those of isostructural alpha-(BEDT-TTF)(2)NH4Hg (SCN)(4), we propose a thermally activated fluctuation of charge order in the metallic phase of alpha-(BEDT-TTF)(2)I-3. This fluctuation was considerably suppressed above 0.65 GPa. The optical conductivity in the metallic phase shows no Drude response.
• Non-Fermi-liquid behavior of the organic superconductor κ-(BEDT-TTF)4Hg2.89Br8 probed by 13C NMR

  Yoshihiro Eto, Megumi Itaya, Atsushi Kawamoto

  Physical Review B - Condensed Matter and Materials Physics 81 21 2010年06月21日 [査読有り][通常論文]
   

  An organic salt, κ- (BEDT-TTF) 4 Hg2.89 Br8 exhibits superconductivity at 4.3 K under ambient pressure suggesting non-Fermi-liquid (NFL) behavior just above Tc. Whereas most organic superconductors are controlled by the bandwidth in the half-filled electron system, this salt realizes a carrier doping away from the half-filled electron system as well as high- Tc cuprates. In order to investigate the origin of NFL behavior, we assessed 13C-NMR measurements in this salt and observed the antiferromagnetic fluctuation as same as in an organic antiferromagnet κ-(BEDT-TTF)2Cu[N(CN)2]Cl with the gap structure. Application of pressure suppresses (T1T)-1 and shifts its maximum to lower temperatures with (T1T)-1 becoming constant above 2 GPa. These results suggest that applying pressure alters the electron system from NFL to FL state and that antiferromagnetic fluctuations contribute to the origin of NFL behavior. © 2010 The American Physical Society.
• Order-disorder type of charge-ordering phase transition in narrow-bandwidth compound, alpha '-(BEDT-TTF)(2)IBr2

  Y. Yue, K. Yamamoto, C. Nakano, M. Uruichi, K. Yakushi, M. Inokuchi, T. Hiejima, A. Kawamoto

  PHYSICA B-CONDENSED MATTER 405 11 S232 - S236 2010年06月 [査読有り][通常論文]
   

  The kinetic energy of alpha'-(BEDT-TTF)(2)IBr2 alpha-(BEDT-TTF)(2)I-3 and alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4) was estimated from the room-temperature optical conductivity measured from 50 to 30 000 cm(-1) The kinetic energy of alpha-(BEDT-TTF)(2)IBr2 was significantly smaller than that of alpha-(BEDT-TTF)(2)I-3 that shows metal-insulator phase transition A clear hysteresis was found in the magnetic susceptibility near the phase transition at around 30 K (C) 2010 Elsevier B V All rights reserved
• SDW phase of (EDT-TTF)(2)AuBr2

  K. Nomura, N. Shimohara, D. Denda, N. Matsunaga, A. Kawamoto

  PHYSICA B-CONDENSED MATTER 405 11 S116 - S119 2010年06月 [査読有り][通常論文]
   

  The low temperature phase in (EDT-TTF)(2)AuBr2 was investigated by H-1 NMR and magnetic susceptibility measurements for protonated and partially deuterated single crystals Two sharp peaks were observed in the temperature dependence of T-1(-1) for both salts associated with the SOW transition T-SDW and the sub-phase transition T* common in the Incommensurate SDW phase The values of T-SDW determined as 15 and 19K for h- and d-salts respectively indicate the negative chemical pressure effect The obtained ratios T*/T-SDW 0 37 and 0 43 for h- and d-salts respectively are slightly larger than the common value T*/T-SDW congruent to 0 3 observed in (TMTCF)(2)X The ratio T*/T-SDW increases for larger T-SDW and the low temperature sub-phase becomes more stable (C) 2009 Elsevier B V All rights reserved
• C-13-NMR study of charge order state of the organic conductor alpha '-(BEDT - TTF)(2)IBr2

  S. Hirose, A. Kawamoto

  PHYSICA B-CONDENSED MATTER 405 11 S160 - S163 2010年06月 [査読有り][通常論文]
   

  It is said that the quasi-two dimensional organic conductor (BEDT - TTF)(2)X forming two columns structure like alpha or theta salts shows charge order (CO) state at low temperature To confirm the existence of the CO state and the electron magnetism in alpha' phase whose symmetry is different from that of alpha and theta phases we investigated C-13-NMR on alpha'-(BEDT - TTF)(2)IBr2 in which one-sided central carbon on BEDT-TTF molecules is substituted with C-13 As a result the change of spectrum was observed at 200 K which corresponds to CO transition and the angular dependence of spectrum at 15 K indicated that the charge ordering pattern was intra-column separating type The spectrum in paramagnetic state can be examined by not only the difference of the charge density on on-site molecule but also the contribution from off-site molecules This result suggested that the hyperfine coupling tensor changes after CO transition in which the charge separates extremely (C) 2010 Published by Elsevier B V
• Charge fluctuation of the superconducting molecular crystals

  T. Yamamoto, Y. Nakazawa, R. Kato, K. Yakushi, H. Akutsu, A. S. Akustu, H. Yamamoto, A. Kawamoto, S. S. Turner, P. Day

  PHYSICA B-CONDENSED MATTER 405 11 S237 - S239 2010年06月 [査読有り][通常論文]
   

  In recent years concern has been raised about the charge fluctuation of the superconducting transition in the loosely dimerized molecular conductors Not only the observation of the charge fluctuation is of considerably important but also the understanding of the mechanism of the fluctuation We have observed degree of charge fluctuation of several beta ''-type ET salts The beta ''-type ET salt is one of the best model compounds because the direction of the largest inter-site Coulomb interaction is perpendicular to that of the largest transfer integral This structural property allows us to examine the role of inter-site Coulomb interaction from the viewpoint of the inter-molecular distance The difference in the molecular charges between the charge rich site and the charge poor sites Delta rho is correlated with the conducting behavior the superconducting materials have the small but finite Delta rho whereas Delta rho of the insulating (metallic) materials is large (almost zero) After the analysis of the configuration in the intermolecular distances, we have found that the degree of fluctuation Delta rho is attributed to the number of the most stable charge distribution(s) N(s) and the number of the energy levels of the allowed charge distribution N(A) The superconducting materials belong to the condition of N(s) >= 2 and N(A) >= 2 Indeed this condition contributes to the fluctuation of the molecular charges (C) 2009 Elsevier B V All rights reserved
• (13) C-NMR study of kappa-(BEDT-TTF)(2) Cu(NCS)(2) under pressure

  M. Itaya, Y. Eto, A. Kawamoto, H. Taniguchi

  PHYSICA B-CONDENSED MATTER 405 11 S259 - S261 2010年06月 [査読有り][通常論文]
   

  We measured the C-13-NMR spectrum and T-1 of kappa-(BEDT - TTF)(2)Cu(NCS)(2) under pressure Both of Knight shift and 1/T1T showed the temperature Independent behavior at low temperature under all pressures therefore It is suggested that this material behaves as Fermi liquid at this region Pressure dependence of Knight shift at low temperature cannot account the strong pressure dependence of the m*(c) which observed by Shubnikov-de Haas (S-dH) measurement On the other hand pressure dependence of Korringa factor calculated from Knight shift and 1/T1T, is similar to that of the m*(c) These results suggest that anti-ferromagnetic (AF) fluctuations contribute to the superconductivity in this material (C) 2010 Elsevier B V All rights reserved
• Dielectric constant in the incommensurate SDW phase of (TMTTF)(2)Br

  Noriaki Matsunaga, Tomonori Akita, Koichi Ichimura, Kazushige Nomura, Atsushi Kawamoto

  PHYSICA B-CONDENSED MATTER 405 11 S108 - S110 2010年06月 [査読有り][通常論文]
   

  The low-frequency dielectric constant was measured in the pressure induced incommensurate SDW phase of (TMTTF)(2)Br in order to investigate the dynamics of the SDW Under the pressure above 0 5 GPa the huge dielectric constant attributed to the motion of the SDW were observed The temperature dependence of the real part of the dielectric constant epsilon whose amplitudes grow with decreasing frequency shows the peak behavior in the Incommensurate SDW phase In contrast of the case of (TMTSF)(2)PF6 the peak temperature of epsilon ' is constant irrespective of the frequency These peak temperature T-P are scaled as T-P/T-SWD similar to 0 3 irrespective of pressure for the pressure larger than 08 GPa and is associated with the sub-phase transition in the incommensurate SOW proposed by the NMR measurement The dielectric properties are probably connected with the co-existence of the CDW component proposed for high temperature sub-phase (C) 2010 Elsevier B V All rights reserved
• Non-Fermi-liquid behavior of the organic superconductor kappa-(BEDT-TTF)(4)Hg2.89Br8 probed by C-13 NMR

  Yoshihiro Eto, Megumi Itaya, Atsushi Kawamoto

  PHYSICAL REVIEW B 81 21 2010年06月 [査読有り][通常論文]
   

  An organic salt, kappa-(BEDT-TTF)(4)Hg2.89Br8 exhibits superconductivity at 4.3 K under ambient pressure suggesting non-Fermi-liquid (NFL) behavior just above T-c. Whereas most organic superconductors are controlled by the bandwidth in the half-filled electron system, this salt realizes a carrier doping away from the half-filled electron system as well as high-T-c cuprates. In order to investigate the origin of NFL behavior, we assessed C-13-NMR measurements in this salt and observed the antiferromagnetic fluctuation as same as in an organic antiferromagnet kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl with the gap structure. Application of pressure suppresses (T1T)(-1) and shifts its maximum to lower temperatures with (T1T)(-1) becoming constant above 2 GPa. These results suggest that applying pressure alters the electron system from NFL to FL state and that antiferromagnetic fluctuations contribute to the origin of NFL behavior.
• Non-fermi liquid behavior of the organic superconductor kappa-(BEDT-TTF)(4)Hg-2 Br-89(8) probed by C-13-NMR

  Yoshihiro Eto, Megumi Itaya, Atsushi Kawamoto

  PHYSICA B-CONDENSED MATTER 405 11 S147 - S149 2010年06月 [査読有り][通常論文]
   

  We assessed C-13-NMR measurements in an organic salt kappa-(BEDT-TTF)(4)Hg-2 Br-89(8) which exhibits superconductivity at 4 3 K under ambient pressure We observed that (T1T)(-1) of H // and perpendicular to layer at ambient pressure increased as the temperature was decreased to 7 K but decreased further at lower temperatures suggesting that the decrease of (T1T)(-1) was not due to the superconductive fluctuations but due to the magnetism of the conduction electrons Application of pressure suppresses (T1T)(-1) with (T1T)(-1) becoming constant above 2 GPa These results suggest that applying pressure alters the electron system from a non-Fermi liquid (NFL) to a Fermi liquid (FL) state and that antiferromagnetic fluctuations contribute to the origin of NFL behavior Whereas most organic conductors show Fermi liquid behavior this salt is an organic superconductor that shows NFL behavior due to the antiferromagnetic fluctuations (C) 2010 Elsevier B V All rights reserved
• Reexamination of C-13-NMR in (TMTTF)(2)AsF6: Comparison with infrared spectroscopy

  Shinji Hirose, Atsushi Kawamoto, Noriaki Matsunaga, Kazushige Nomura, Kaoru Yamamoto, Kyuya Yakushi

  PHYSICAL REVIEW B 81 20 2010年05月 [査読有り][通常論文]
   

  The charge order (CO) state can be observed by microprobe measurements such as nuclear magnetic resonance (NMR) and infrared spectroscopy. We used the infrared spectroscopy to examine (TMTTF)(2)AsF6 and confirmed the CO transition seen in previous C-13-NMR studies. However we found the degree of charge disproportionation, Delta rho = 0.16, to be smaller than that obtained from the analysis of T-1 in C-13-NMR and the redistribution of charge density below spin Peierls transition predicted by C-13-NMR was not observed at low temperature. We estimated the degree of spin disproportionation to be 0.11 from the analysis of the NMR shift in previous NMR studies. This small disproportionation does not require the redistribution of charge density at low temperature. The different behaviors of T-1 at charge-rich and charge-poor molecular sites observed by C-13-NMR can be examined by the contribution of the commensurate antiferromagnetic fluctuation with 4k(F).
• Antiferromagnetic phase in beta '-(BEDT-TTF)(2)ICl2 under pressure as seen via C-13 NMR

  Yoshihiro Eto, Atsushi Kawamoto

  PHYSICAL REVIEW B 81 2 2010年01月 [査読有り][通常論文]
   

  We assessed carbon-13 nuclear magnetic resonance (C-13 NMR) measurements of the layered organic salt beta'-(BEDT-TTF)(2)ICl2, which exhibits antiferromagnetic transition at ambient pressure and 22 K and superconductive transition at 8.2 GPa and 14.2 K (the highest known superconductive transition temperature among organic superconductors). By analyzing the C-13 NMR spectrum with the tensor, we determined the antiferromagnetic moment of this salt to be mu(B) per dimer at ambient pressure, strongly indicating that this salt is a dimer Mott insulator. From NMR measurements under pressure, we found that the structure of the antiferromagnetic phase changed at 0.6 GPa. The moment of this antiferromagnetic phase was estimated to be 0.47 mu(B) per dimer at 0.6 GPa and 26 K. In addition, applying pressure rapidly decreased the spin susceptibility in the paramagnetic state, and the pressure dependence of T-N showed anomalous behavior consistent with theoretical proposals, including dimensional crossover.
• Evidence for exchange interaction between donor and acceptor layers in B’-(BEDT-TTF)(TCNQ)

  Yoshihiro Eto, Atsushi Kawamoto, Noriaki Matsunaga, Kazushige Nomura, Kaoru Yamamoto, Kyuya Yakushi

  Phys. Rev. B 80 17 174506  2009年11月 [査読有り][通常論文]
  
• Evidence for exchange interaction between donor and acceptor layers in beta(')-(BEDT-TTF)(TCNQ)

  Eto Yoshihiro, Kawamoto Atsushi, Matsunaga Noriaki, Nomura Kazushige, Yamamoto Kaoru, Yakushi Kyuya

  PHYSICAL REVIEW B 80 17 2009年11月 [査読有り][通常論文]
   

  We assessed the infrared-absorption spectra and C-13-NMR measurements in a layered organic salt, beta(')-(BEDT-TTF)(TCNQ), which exhibits antiferromagnetic transitions at 20 and 3 K. The former originates from the spin in the bis-(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) layers, while the latter originates from the localized spin in the tetracyanoquinodimethane (TCNQ) layers. Using infrared-absorption spectroscopy, we estimated the degree of charge transfer, rho, between BEDT-TTF and TCNQ as 0.5. Using C-13-NMR spectroscopy, we observed an exchange field at the BEDT-TTF site, which is produced by the localized spins of TCNQ dimers. Using the obtained value of rho and the molecular arrangement of beta(')-(BEDT-TTF)(TCNQ), which is similar to that of the highest T-c organic superconductor, beta(')-(BEDT-TTF)(2)ICl2, we concluded that the absence of the pressure-induced superconductivity in beta(')-(BEDT-TTF)(TCNQ) results from the presence of this exchange field. The exchange interaction, J, and the exchange field, H-ex, were estimated as -12 K and -19 T/mu(B) on the TCNQ dimer unit, respectively. These findings suggest that superconductivity may arise in beta(')-(BEDT-TTF)(TCNQ) by the application of an external field of 19 T under high pressure.
• C-13 NMR study on the charge-ordering salt alpha '-(BEDT-TTF)(2)IBr2

  Shinji Hirose, Atsushi Kawamoto

  PHYSICAL REVIEW B 80 16 2009年10月 [査読有り][通常論文]
   

  Among quasi-two-dimensional organic conductors, (BEDT-TTF)(2)X, what form the two column structure of alpha or theta is thought to show a charge-ordering insulating state. The alpha' modification is the other candidate for a charge-ordering state. To determine the existence of a charge-ordering state and electron magnetism in the alpha' phase, which has a symmetry that differs from that of the alpha and theta phases, we utilized C-13-NMR to examine alpha'-(BEDT-TTF)(2)IBr2 in which one side of the central carbon on the BEDT-TTF molecule is substituted with C-13 nuclei. We observed changes in its spectrum at 200 K. The angular dependence of the NMR shift at 15 K indicated that the charge-ordering pattern is intracolumn disproportionation and the ratio of charge disproportionation on the spin-poor site and spin-rich sites is almost 1:0. The angle dependence of NMR spectrum at 60 K suggests that the hyperfine coupling tensor in the paramagnetic charge-ordering state is determined not only by the charge density of on-site molecules but also by the contribution of off-site molecules. The change in hyperfine coupling tensor must be taken into account in NMR studies of the paramagnetic CO state.
• C-13-NMR Study of Charge Ordering State in the Organic Conductor, alpha-(BEDT-TTF)(2)I-3

  Takuma Kawai, Atsushi Kawamoto

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 7 2009年07月 [査読有り][通常論文]
   

  The pattern of charge ordering of the quasi two-dimensional organic conductor, alpha-(BEDT-TTF)(2)I-3 [BEDT-TTF: bis(ethylenedithio)tetrathiafulevalene], provides important information about the usual transport properties of this salt. Experiments on this salt have yielded conflicting results. Especially, the results of nuclear magnetic resonance (NMR) measurement and X-ray Diffraction (XRD) study have suggested contradictory charge patterns. To clarify these discrepancies, we performed C-13-NMR measurements using a single side C-13 enriched molecule. Above the metal-insulator transition temperature, the spin susceptibility at the B site decreased and that at the C site increased with decreasing temperature. Below the metal-insulator (M-I) transition temperature, however, the angular dependence of the NMR shift suggested that the charge order pattern was a horizontal stripe, in which the A(A') and B Molecules are charge rich sites and the A'(A) and C molecules are charge poor.
• Antiferromagnetic Fluctuations in the Organic Superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2) under Pressure

  Megumi Itaya, Yoshihiro Eto, Atsushi Kawamoto, Hiromi Taniguchi

  PHYSICAL REVIEW LETTERS 102 22 2009年06月 [査読有り][通常論文]
   

  We measured the C-13-NMR spectrum and T-1 of the quasi-two-dimensional organic superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2) under pressure. This material was thought to show a relationship between T-c and the effective cyclotron mass m(c)(*), obtained from the Shubnikov-de Haas (SdH) effect. We found that kappa-(BEDT-TTF)(2)Cu(NCS)(2) behaved as a Fermi liquid at low temperature under all pressures, and antiferromagnetic fluctuations were expected. The pressure dependence of the Korringa factor is similar to that of the effective cyclotron mass m(c)(*), suggesting that antiferromagnetic fluctuations contribute to the superconductivity of this material. We also found that, under pressure, T-* was shifted to 150 K, the temperature characteristic of the shift from bad metal to good metal.
• Charge Order-Disorder Phase Transition in alpha '-[Bis(ethylenedithio)tetrathiafulvalene](2)IBr2 [alpha '-(BEDT-TTF)(2)IBr2]

  Yue Yue, Chikako Nakano, Kaoru Yamamoto, Mikio Uruichi, Roman Wojciechowski, Makoto Inokuchi, Kyuya Yakushi, Atushi Kawamoto

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 4 2009年04月 [査読有り][通常論文]
   

  We present the anomalies at similar to 200 K in electrical resistivity, transmittance and reflectance in the far-infrared region, and the magnetic susceptibility of alpha'-(BEDT-TTF)(2)IBr2 [BEDT-TTF = bis(ethylene-dithio)tetrathiafulvalene]. This phase transition is investigated by infrared, Raman, and far-infrared spectroscopies. Through the spectroscopic investigation, we found that the positive charges on BEDT-TTF molecules are strongly localized owing to a strong Coulomb interaction in both low-temperature (LT) and high-temperature (HT) phases. We show the spectroscopic data that suggest the charge order in the LT phase and the charge disorder in the HT phase. The phase transition at similar to 200K in alpha'-(BEDT-TTF)(2)IBr2 is the charge order-disorder phase transition not accompanied by Structural changes. On the basis of the localized Picture, we qualitatively interpreted the experimental results above and below the phase transition. The effect of hydrostatic pressure was investigated by electrical resistivity Measurement and Raman spectroscopy. The charge-ordered State is Successively Suppressed by applying hydrostatic pressures of up to 1.2 GPa. The resistivity and Raman spectrum qualitatively change above 1.4 GPa. We speculate that the phase transition changes the character from a charge order-disorder to a metal-insulator.
• Hall effect in the SDW phase of quasi-one-dimensional organic conductor (TMTTF)(2)Br

  Noriaki Matsunaga, Takehito Satoh, Koichi Ichimura, Kazushige Nomura, Atsushi Kawamoto

  PHYSICA B-CONDENSED MATTER 404 3-4 389 - 391 2009年03月 [査読有り][通常論文]
   

  The resistance and Hall resistance measurements have been carried out in the organic compound (TMTTF)(2)Br for various pressures. For the incommensurate SDW phase of (TMTrF)(2)Br stabilized above 0.5 GPa, the sign reversal of the Hall resistance was observed with decreasing temperature. In addition, a large hysteresis of the Hall resistance was observed above T*similar to 0.3T(SDW), where T-SDW is the SDW transition temperature. This behavior is possibly related to the sub-phase structure of incommensurate SDW phase, where the coexistence of the charge-density wave with the SDW was proposed for high temperature sub-phase. On the other hand, this type of hysteresis is not observed in the (TMTSF)(2)PF6 compound. These differences in both salts can be explained by taking into account the difference of the ratio of charge-density wave for high temperature sub-phase. (C) 2008 Elsevier B.V. All rights reserved.
• Charge disproportionation and inversion symmetry breaking in organic conductor alpha-(BEDT-TTF)(2)RbHg(SCN)(4)

  Takuma Kawai, Atsushi Kawamoto

  PHYSICAL REVIEW B 78 16 2008年10月 [査読有り][通常論文]
   

  The quasi-two-dimensional organic conductor alpha-(BEDT-TTF)(2)RbHg(SCN)(4) has been investigated by (13)C-NMR using a field parallel to the ac plane of 9.4 T. We observed no enhancement of (T(1)T)(-1) at 12 K or isotropic reduction of spin susceptibility below 12 K, indicating that spin-density wave formation did not occur at 12 K. Above 100 K, a decrease of spin susceptibility was observed at the C site and a complementary increase was observed at the A and A(') sites, suggesting charge disproportionation due to off-site Coulomb interactions. Below 12 K, the spectrum showed broadening and splitting of peaks. These findings indicate that inversion symmetry breaking in charge-density wave instability occurs at low temperatures.
• Calorimetric study of molecular superconductor kappa-(BEDT-TTF)(2)Ag(CN)(2)H2O which contains water in the anion layers

  T. Ishikawa, S. Yamashita, Y. Nakazawa, A. Kawamoto, M. Oguni

  JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY 92 2 435 - 438 2008年05月 [査読有り][通常論文]
   

  Thermodynamic investigation of an organic superconductor kappa-(BEDT-TTF)(2)Ag(CN)(2)H2O in which the BEDT-TTF dimers are arranged in the K-type structure in the donor layers is performed by the relaxation calorimetric technique at low temperatures and under magnetic fields. A thermal anomaly related to the superconductive phase transition was observed at 5 K. The existence of residual gamma* in the superconductive state is about 18% of the normal state gamma value, which is larger than those of kappa-(BEDT-TTF)(2)Cu(NCS)(2), and kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br salt. The lattice heat capacity reflected on the beta-term in the low-temperature heat capacity was found to be affected by the cooling rate. The disorder produced in the network structure constructed by hydrogen bond in the insulating layer is considered to give low-energy phonon excitations reflected in the heat capacity.
• Charge-ordering phase transition in α'-(BEDT-TTF)2IBr2

  Y. Yue, C. Nakano, K. Yamamoto, M. Uruichi, K. Yakushi, A. Kawamoto

  JOURNAL OF PHYSICS: CONFERENCE SERIES 132 12007  2008年 [査読有り][通常論文]
   

  The phase transition found in the electrical resistivity of α'-(BEDT-TTF)2IBr2 was investigated by observing the charge-sensitive phonon modes of BEDT-TTF. The low-temperature phase was elucidated to be a charge-ordered state with large amplitude. The pattern of charge-order was a horizontal or diagonal stripe, which requires the breaking of inversion symmetry. The breaking of symmetry was confirmed by observing the asymmetric stretching mode of IBr2-. The symmetry breaking occurs primarily at -200 K rather continuously. It was proposed in the high-temperature phase that the nearly localized charges are dynamically fluctuating individually or collectively with a fluctuation rate much slower than 55 cm-1. ? 2008 IOP Publishing Ltd.
• Thermodynamic study of κ-(BEDT-TTF)2Ag(CN)2H2O under pressures and with magnetic fields

  Tokoro Nozomi, Kubota Osamu, Yamashita Satoshi, Kawamoto Atsushi, Nakazawa Yasuhiro

  Journal of Physics: Conference Series 132 1 012010/1 - 012010/8 2008年 [査読有り][通常論文]
   

  A low-temperature thermodynamic investigation on an organic superconductor κ-(BEDT-TTF)2Ag(CN)2H2O is performed under pressure and with magnetic fields. Using the ac-modulation technique available under pressures, we have succeeded to detect the thermal anomaly being associated with the superconducting transition. The thermal anomaly was found to be sensitive to the external magnetic fields at ambient pressure. We have observed that this anomaly disappears under pressure of 0.4 GPa which suggests that the superconducting ground state is transformed into the normal metallic state by the application of the pressure. The observed feature is consistent with the scenario of Mott-Hubbard physics realized due to the strong electron correlations in the dimerized BEDT-TTF salts. © 2008 IOP Publishing Ltd.
• Inhomogeneous site charges at the boundary between the insulating, superconducting, and metallic phases of beta '-type bis-ethylenedithio-tetrathiafulvalene molecular charge-transfer salts

  Hiroshi M. Yamamoto, Yamamoto, Takashi, Yamamoto, Hiroshi M., Kato, Reizo, Uruichi, Mikio, Yakushi, Kyuya, Akutsu, Hiroki, Sato-Akutsu, Akane, Kawamoto, Atsushi, Turner, Scott S., Day, Peter

  Physical Review B 77 20 2008年 [査読有り][通常論文]
   

  We have examined time-averaged charges of the molecular donors around the phase boundary between the insulating, superconducting, and metal phases for beta ''-type ET [ET=bis-ethelenedithio-tetrathiafulvalene] salts with one (two) hole(s) per two (three) molecules by using vibrational spectroscopy. Around the phase boundary, the site charges are neither those expected for a well-developed charge-ordered (CO) state nor a homogeneous distribution. The molecular charges exhibit an inhomogeneous distribution just above the insulator-superconductor transition temperature. We have analyzed the distribution of the site charges from the viewpoint of the alternation of intersite Coulomb interactions along the stacking direction. The closeness in the energy of several CO patterns mostly contributes to the inhomogeneous distribution, whereas a large difference (no difference) in the energy levels contributes to the CO (homogeneous) state. Our observations indicate that the instability due to the closeness in the energy of several distributions correlates with the insulator-superconductor transition in nondimerized or weakly dimerized molecular conductors.
• Pressure dependence of the phase separation in deuterated κ - (BEDT - TTF)2 Cu [N (CN)2] Br at the Mott boundary

  S. Kimura, T. Nishi, T. Takahashi, T. Mizuno, K. Miyagawa, H. Taniguchi, A. Kawamoto, K. Kanoda

  Journal of Magnetism and Magnetic Materials 310 2 1102 - 1104 2007年03月 [査読有り][通常論文]
   

  The pressure dependence of the optical reflectivity spectrum [R (ω)] of deuterated κ - (BEDT - TTF)2 Cu [N (CN)2] Br (d 44) at T = 4.5 K was determined. At the ambient pressure, d 44 under fast cooling conditions forms an antiferromagnetic insulator (AFI) phase, as confirmed by the wavenumber of the ν3 (ag) vibration mode. At the pressures in the range of several MPa, the optical spectrum changes to that of a metal that matches a non-deuterated material consisting of AFI and PM (paramagnetic metallic) spectra. This indicates that the phase separation between the AFI and PM phases appears at intermediate pressures. The phase size of the separated phase is smaller than the instrumental spatial resolution of 50 μ m, based on the inability of our methods to record it. © 2006 Elsevier B.V. All rights reserved.
• Magnetic-field-induced superconductor-insulator-metal transition in an organic conductor: An infrared magneto-optical imaging spectroscopic study

  Tatsuhiko Nishi, Shin-Ichi Kimura, Toshiharu Takahashi, Hojun Im, Yong-Seung Kwon, Takahiro Ito, Kazuya Miyagawa, Hiromi Taniguchi, Atsushi Kawamoto, Kazushi Kanoda

  Physical Review B - Condensed Matter and Materials Physics 75 1 2007年 [査読有り][通常論文]
   

  The magnetic-field-induced superconductor-insulator-metal transition (SIMT) in partially deuterated κ- (BEDT-TTF)2 Cu [N (CN)2] Br, which is just on the Mott boundary, has been observed using the infrared magneto-optical imaging spectroscopy. The infrared reflectivity image on the sample surface revealed that the metallic (or superconducting) and insulating phases coexist and they have different magnetic-field dependences. One of the magnetic-field dependence is SIMT that appeared on part of the sample surface. The SIMT was concluded to originate from the balance of the inhomogeneity in the sample itself and the disorder of the ethylene end groups resulting from fast cooling. © 2007 The American Physical Society.
• Suppression of inhomogeneous electron localization in kappa-(BEDT-TTF)(2)Cu-2(CN)(3) under pressure

  Atsushi Kawamoto, Yosuke Honma, Ken-ichi Kumagai

  PHYSICAL REVIEW B 74 21 2006年12月 [査読有り][通常論文]
   

  In order to investigate the nature of the insulator phase of kappa-(BEDT-TTF)(2)Cu-2(CN)(3) [where BEDT-TTF represents bis(ethylenedithio)terathiofulvalene] and why this salt is a superconductor under pressure but not under ambient pressure, we examined the C-13 NMR spectra and spin lattice relaxation rate of kappa-(BEDT-TTF)(2)Cu-2(CN)(3) under pressure. The spin susceptibility evaluated from the Knight shift decreased with increase in pressure, and line broadening was suppressed above a critical pressure. The temperature dependence of (T1T)(-1) for kappa-(BEDT-TTF)(2)Cu-2(CN)(3) above a critical pressure was that for kappa-(BEDT-TTF)(2)X, where X was Cu[N(CN)(2)]Br or Cu(NCS)(2). These results suggest that the electronic structure of kappa-(BEDT-TTF)(2)Cu-2(CN)(3) under pressure is similar to that of other kappa-(BEDT-TTF)(2)X salts. The results support our model that electron inhomogeneity and hopping conduction, which are common features of semiconductivity in kappa-(BEDT-TTF)(2)X at high temperatures, are responsible for the insulator phase in kappa-(BEDT-TTF)(2)Cu-2(CN)(3). The electron inhomogeneity suppresses the semiconductor-metal transformation and superconductivity observed in other kappa-(BEDT-TTF)(2)X salts.
• Suppression of inhomogeneous electron localization in kappa-(BEDT-TTF)(2)Cu-2(CN)(3) under pressure

  Kawamoto Atsushi, Honma Yosuke, Kumagai Ken-ichi

  PHYSICAL REVIEW B 74 21 2006年12月 [査読有り][通常論文]
  
• mu SR study of an antiferromagnetic Mott insulator beta '-(BEDT-TTF)(2)ICl2

  K Satoh, H Taniguchi, A Kawamoto, W Higemoto

  PHYSICA B-CONDENSED MATTER 374 99 - 101 2006年03月 [査読有り][通常論文]
   

  Zero-field mu SR measurements on the antiferromagnetic Mott insulator beta'-(BEDT-TTF)(2)ICl2 were performed in order to study the microscopic magnetic properties of this organics. The volume fraction of the antiferromagnetic phase was found to be temperature independent. Muon precession frequency, which is proportional to the magnitude of the magnetic moment at the dimer of two BEDT-TTF molecules, does not follow the simple model based on the mean-field approximation. (c) 2005 Elsevier B.V. All rights reserved.
• Scanning tunneling spectroscopy on organic superconductors

  K Ichimura, K Nomura, A Kawamoto

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 3B 2264 - 2267 2006年03月 [査読有り][通常論文]
   

  The superconducting phase of organic superconductors (BEDT-TTF)(2)X was Studied by electron tunneling using scanning tunneling microscope (STM). Tunneling both at the conducting plane and lateral surfaces was performed on single crystals of (BEDT-TTF)(2)Cu(NCS)(2). The tunneling conductance curve obtained at the conducting plane is explained by d-wave gap symmetry. Tunneling spectra at lateral surfaces vary depending on the tunneling direction, suggesting the in-plane anisotropy of the gap. The directional dependence is also consistent with d-wave symmetry with line nodes pi/4 from the k(b)- and k(c)-axes. This indicates that the superconducting pair wave function has d(x2-y2)-wave symmetry. Protonated and partially deuterated (BEDT-TTF)(2)Cu(CN)(2)]Br samples were also studied. Tunneling spectra are consistent with d-wave symmetry in all salts. Gap parameters are obtained as functions of the effective correlation. The large gap value suggests the strong coupling Superconductivity. The zero-bias conductance peak, which is evidence for nodes of the superconducting gap, was found.
• Incoherent-coherent crossover behavior in κ-(BEDT-TTF) 2 X, probed by 13C-NMR and optical studies

  A. Kawamoto, Y. Honma, K. Kumagai, K. Yamamoto, K. Yakushi

  Journal of Low Temperature Physics 142 3-4 523 - 526 2006年02月 [査読有り][通常論文]
   

  We have measured 13C-NMR and reflection spectrum in κ-(BEDTTTF) 2Ag(CN) 2·H 2O. No increase of the AF magnetic fluctuation as in κ-(BEDT-TTF) 2Cu[N(CN) 2]C was observed. Results of 13C-NMR suggested the emergence of superconductivity does not require the increase of the AF magnetic fluctuation, but a crossover to the Fermi liquid regime. Optical studies suggested the crossover corresponds to the development of the coherence of conduction electrons. © Springer Science+Business Media, Inc. 2007.
• Crystal growth of 50mg-class single crystals of beta '-(BEDT-TTF)(2)ICl2 and crystal evaluation

  H. Taniguchi, R. Sato, K. Satoh, A. Kawamoto, H. Okamoto, T. Kobayasi, K. Mizuno

  JOURNAL OF LOW TEMPERATURE PHYSICS 142 3-4 437 - 440 2006年02月 [査読有り][通常論文]
   

  Single crystals of beta'-(BEDT-TTF)(2)ICl2 were grown electrochemically. In the crystal growth we used a large glass cell of which inner volume was more than 200ml. In addition, the solution was replaced by newly prepared one every two months where total period of synthesis was about one year. As a result we obtained a number of large crystals over 10mg. The weight of the largest crystal is about 50mg. The crystallinity was confirmed by X-ray topograph imaging.
• Incoherent-coherent crossover behavior in kappa-(BEDT-TTF)(2)X, probed by C-13-NMR and optical studies

  A. Kawamoto, Y. Homna, K. Kumagai, K. Yamamoto, K. Yakushi

  JOURNAL OF LOW TEMPERATURE PHYSICS 142 3-4 519 - 522 2006年02月 [査読有り][通常論文]
   

  We have measured C-13-NMR and reflection spectrum in K-(BEDT-TTF)(2)Ag(CN)(2)(H2O)-H-.. No increase of the AF magnetic fluctuation as in K-(BEDT-TTF)(2)Cu[N(CN)(2)]C was observed Results of C-13-NMR suggested the emergence of superconductivity does not require the increase of the AF magnetic fluctuation, but a crossover to the Fermi liquid regime. Optical studies suggested the crossover corresponds to the development of the coherence of conduction electrons.
• Charge ordered state in (BEDT-TTF)(3)Cl-2 center dot 2H(2)O

  T. Ogura, A. Kawamoto, K. Kumagai, H. Taniguchi

  JOURNAL OF LOW TEMPERATURE PHYSICS 142 3-4 543 - 546 2006年02月 [査読有り][通常論文]
   

  The quasi-two-dimensional (Q2D) organic conductor (BEDT-TTF)(3)Cl-2 center dot 2H(2)O is metallic at 300 K and it undergoes a metal-insulator transition (MIT) at T similar to 140 K as revealed from magnetic susceptibility and MRelectric conductivity measurements. Using C-13-NMR measurement, we observed a split of the NMR spectrum which corresponds to a charge rich and poor site below the MIT temperature and concluded that the insulator state is in a charge ordered (CO) state, instead of a charge density wave (CD W) formation proposed previously.
• SQUID-magnetometry study of the P-T phase diagram of kappa-[(BEDT-TTF)(1-x)(BEDSe-TTF)(x)](2)Cu[N(CN)(2)]Br

  Y. V. Sushko, S. O. Leontsev, O. B. Korneta, A. Kawamoto

  JOURNAL OF LOW TEMPERATURE PHYSICS 142 3-4 563 - 566 2006年02月 [査読有り][通常論文]
   

  Static susceptibility of kappa-[(BEDT-TTF)(1-x)(BEDSe-TTF)(x)](2)Cu[N(CN)(2)]Br alloys with the BEDSe-TTF content near the border-line of ambient pressure superconductivity (x similar to 0.3) has been measured as a function of temperature, magnetic field, and pressure. The results are discussed in comparison with the data on a family of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl1-xBrx.
• Unusual electronic state of layered theta-(ET)(2)X studied by Raman spectroscopy

  K. Yakushi, K. Suzuki, K. Yamamoto, T. Yamamoto, A. Kawamoto

  JOURNAL OF LOW TEMPERATURE PHYSICS 142 3-4 659 - 662 2006年02月 [査読有り][通常論文]
   

  Employing Raman spectroscopy, we have studied the electronic structure of the charge-ordering system, theta-(ET)(2)X the dihedral angle (phi) of which ranges from 100 degrees to 121 degrees. The most stable metal, theta-(ET)(2)I-3, (phi=100 degrees) has a uniform charge distribution in a whole temperature range. The compounds with phi > 111 degrees have an inhomogeneous charge distribution even above the CO transition, which implies that the charges have localized nature in a whole temperature range. These localized charges are long-range ordered in the CO phase, whereas they are fluctuating randomly or forming short-range ordered domains above the CO phase transition.
• Charge ordering state of β″ - (ET)3 (HS O4) 2 and β″ - (ET)3 (Cl O4) 2 by temperature-dependent infrared and Raman spectroscopy

  Takashi Yamamoto, Takashi Yamamoto, Mikio Uruichi, Kyuya Yakushi, Atsushi Kawamoto

  Physical Review B - Condensed Matter and Materials Physics 73 12 2006年 [査読無し][通常論文]
   

  We present the temperature-dependent infrared and Raman spectra of β″ - (ET)3 X2 (X=HS O4 and Cl O4; ET=bis -ethylenedithio- tetrathiafulvalene) compounds which undergo a metal-insulator transition. The infrared-active v27 mode discontinuously split into two bands at the metal-insulator transition temperature of 127 K in the X=HS O4 salt, whereas, the corresponding mode continuously changed across the metal-insulator transition temperature of ∼170 K in the X=Cl O4 salt. In both compounds, the charge-sensitive v27 mode split into two in the insulating phase. This drastic spectral change indicates that the metal-insulator transition originated in the charge ordering. Employing the frequencies of the split v27 bands, the site charges are estimated to be + 0.34 and + 0.81 for X=HS O4 and + 0.36 and + 0.81 for X=Cl O4. We also estimated the site charges using the Raman-active v2 mode and obtained consistent results. Examining the selection rule of the v3 mode, we reached the conclusion that the unit cell with space group P1 has a pseudoinversion center in the charge-ordered phase. Based on the symmetry, we propose a charge-ordering pattern for the X=HS O4 and X=Cl O4 salts, which is quite different from that of the X=Re O4 salt reported previously. We qualitatively discuss the differences in the charge-ordering pattern considering the anisotropic intersite Coulomb interaction. © 2006 The American Physical Society.
• Tunneling spectroscopy on partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br By STM

  Koichi Ichimura, Kazushige Nomura, Atsushi Kawamoto

  LOW TEMPERATURE PHYSICS, PTS A AND B 850 607 - + 2006年 [査読有り][通常論文]
   

  The superconducting phase of organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br was studied by the electron tunneling using STM. Tunneling spectra were obtained at partially deuterated kappa-(BEDT-TTF-d[3,3])(2)Cu[N(CN)(2)]Br. The tunneling conductance curve exhibits clear superconducting gap structure. Tunneling spectra with linear dependence on the energy are explained by d-wave pairing. We obtained the gap parameter as a function of the effective correlation strength, which can be controlled by partial deuteration. The large gap value suggests strong coupling superconductivity. Moreover, a zero bias conductance peak (ZBCP) was found in d[3,3] salt. d-wave pairing in kappa-(BEDT-TTF)(2)X is strongly supported.
• Vibrational spectra of beta ''-(ET)(3)X-2 (X = HSO4, ClO4) salts

  T Yamamoto, M Uruichi, K Yamamoto, K Yakushi, A Kawamoto

  SYNTHETIC METALS 155 3 628 - 630 2005年12月 [査読有り][通常論文]
   

  The IR and Raman spectra of beta"-(ET)(3)X-2 [X = HSO4 and ClO4] salts were measured at various temperatures below 300 K. The nu(2) and nu(27) modes exhibit the splitting into two peaks below the metal-insulator transition temperature. This phenomenon is ascribed to the charge ordered (CO) state. The CO patterns of the presented compounds were determined on the basis of the numerical calculation of the vibronic nu(3L) mode. The assignment of the nu(27) mode of ET+ was confirmed through the measurement of the reflectance spectra of the 1:1 salts (ET)ClO4, (ET)AuCl2Br2 and the isotope analogues. The nu(27) mode is the efficient probe to the site charges of the ET salts. (C) 2005 Published by Elsevier B.V.
• Infrared and Raman studies of theta-(BEDT-TTF)(2)CsZn(SCN)(4): Comparison with the frozen state of theta-(BEDT-TTF)(2)RbZn(SCN)(4)

  K Suzuki, K Yamamoto, K Yakushi, A Kawamoto

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 9 2631 - 2639 2005年09月 [査読有り][通常論文]
   

  We present the optical conductivity and Raman spectra of theta-(BEDT-TTF)(2)CsZn(SCN)(4). The vibrational and vibronic bands in the 1200-1600cm(-1) region was assigned with the aid of the C-13- substituted compound. The nearly uniform charge distribution was found in a whole temperature range from 300 to 6 K. However, the space group symmetry I222 is locally broken already at room temperature. The broken symmetry suggests the resemblance to the high-temperature phase and frozen state of theta-(BEDT-TTF)(2)RbZn(SCN)(4), which consists of short-range ordered charge-ordering domains. The amplitude in the charge-ordering domain of theta-(BEDT-TTF)(2)CsZn(SCN)(4) is extremely small in a whole temperature range. At room temperature, hydrostatic pressure narrows the bandwidth of theta-(BEDT-TTF)(2)CsZn(SCN)(4) to enlarge the amplitude in short-ranged ordered domains. The long-range ordered charge ordering in theta-(BEDT-TTF)(2)CsZn(SCN)(4) Was found at 10 K under the hydrostatic pressure of 2.5 GPa.
• Scanning tunneling spectroscopy on kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

  K Ichimura, S Higashi, K Nomura, A Kawamoto

  SYNTHETIC METALS 153 1-3 409 - 412 2005年09月 [査読有り][通常論文]
   

  We report the electron tunneling spectroscopy on partially deuterated kappa-(BEDT-TTF-d[3,3])(2)Cu[N(CN)(2)]Br using a low temperature STM. In the superconducting state, tunneling spectra show the energy gap structure clearly; the conductance around the zero bias voltage is well reduced. V-shaped tunneling conductance curve inside the gap edge suggests the gap anisotropy. The linear dependence on the energy near zero bias is explained by the d-wave pairing with line nodes. By fitting to the d-wave gap model, we obtain the gap parameter as Delta=1.4-3.3 meV. Correspondingly, 2 Delta/kT(c) is estimated as 2.7-6.4. The value is almost the same as that in kappa-(BEDT-TTF)(2)Cu(NCS)(2), d[0,0] and d[2,2] salts. The zero bias anomaly, which is an evidence for nodes of the superconducting gap, was found. The d-wave symmetry is strongly supported.
• Examination of the charge-sensitive vibrational modes in bis(ethylenedithio)tetrathiafulvalene

  Takashi Yamamoto, Mikio Uruichi, Kaoru Yamamoto, Kyuya Yakushi, Atushi Kawamoto, Hiromi Taniguchi

  Journal of Physical Chemistry B 109 32 15226 - 15235 2005年08月18日 [査読有り][通常論文]
   

  We reinvestigated the two C=C stretching modes of the five-membered rings of ET (ET = bis(ethylenedithio)-tetrathiafulvalene), namely, v2 (in-phase mode) and v27 (out-of-phase mode). The frequency of the v27 mode of ET+ was corrected to be ∼1400 cm -1, which was identified from the polarized infrared reflectance spectra of (ET)(ClO4), (ET)(AuBr2Cl2), and the deuterium- or 13C-substituted compounds of (ET)(AuBr 2Cl2). It was clarified from DFT calculations that the frequency of the v27 mode of the flat ET0 molecule was significantly different from that of the boat-shaped ET0 molecule. We obtained the linear relationship between the frequency and the charge on the molecule, ρ, for the flat ET molecule, which was shown to be v 27(ρ) = 1398 + 140(1 - ρ) cm-1. The frequency shift due to oxidation is remarkably larger than that reported in previous studies. The fractional charges of several ET salts in a charge-ordered state can be successfully estimated by applying this relationship. Therefore, the v27 mode is an efficient probe to detect ρ in the charge-transfer salts of ET. Similarly, a linear relationship for the v2 mode was obtained as v2(p) = 1447 + 120(1 - ρ). This relationship was successfully applied to the charge-poor molecule of θ-type ET salts in the charge-ordered state but could not be applied to the charge-rich molecule. This discrepancy was semiquantitatively explained by the hybridization between the v2 and v3 modes. © 2005 American Chemical Society.
• The origin of the phase separation in partially deuterated kappa-(ET)(2)Cu[N(CN)(2)]Br studied by infrared magneto-optical imaging spectroscopy

  T Nishi, S Kimura, T Takahashi, T Ito, HJ Im, YS Kwon, K Miyagawa, H Taniguchi, A Kawamoto, K Kanoda

  SOLID STATE COMMUNICATIONS 134 3 189 - 193 2005年04月 [査読有り][通常論文]
   

  The direct observation of the phase separation between the metallic and insulating states of 75%-deuterated kappa-(ET)(2)Cu[N(CN)(2)]Br (d33) using infrared magneto-optical imaging spectroscopy is reported, as well as the associated temperature, cooling rate, and magnetic field dependencies of the separation. The distribution of the center of spectral weight (<omega >) of d33 did not change under any of the conditions in which data were taken and was wider than that of the non-deuterated material. This result indicates that the inhomogenity of the sample itself is important as part of the origin of the metal-insulator phase separation. (c) 2005 Elsevier Ltd. All rights reserved.
• Influence of the cooling rate on low-temperature Raman and infrared-reflection spectra of partially deuterated kappa-(BEDT-TTF)(2)Cu(N(CN)(2))Br

  A Maksimuk, K Yakushi, H Taniguchi, K Kanoda, A Kawamoto

  SYNTHETIC METALS 149 1 13 - 18 2005年02月 [査読有り][通常論文]
   

  Raman and infrared-reflection spectra of kappa-(BEDT-TTF)(2)Cu(N(CN)(2))Br and its denterated and partially deuterated analogues were measured at temperatures between 5 and 300 K and cooling rates from 1 to 20 K/min. It was found that, in partially deuterated samples, the interdimer electron-molecular vibration splitting of v(3) mode in Raman spectra, and linewidths of some phonon peaks both in Raman and infrared spectra depend on the cooling rate. These observations were explained by disorder-related effects. (C) 2004 Elsevier B.V. All rights reserved.
• Field-induced metal-insulator transition in partially deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br

  Atsushi Kawamoto, Masato Yamasita, Ken-Ichi Kumagai

  Physical Review B - Condensed Matter and Materials Physics 70 21 1 - 4 2004年12月 [査読有り][通常論文]
   

  A 13C-NMR study on nondeuterated and partially deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br is reported, where BEDT-TTF is bis(ethylenedithio)tetra-thiafulvalene. By using a BEDT-TTF molecule with 13C as one of its central carbons, we could estimate the density of states from the Knight shift and the spin-lattice relaxation rate. Although the reduced mass effect predicted from the specific-heat measurement was not observed in the 13C-NMR spectrum, a metal-to- antiferromagnetic phase transition was observed with a phase separation at around 18 K on the half-deuterated κ-(BEDT-TTF)2Cu[N(CN) 2]Br under a high magnetic field. No such transition occurred in the half-deuterated salt under a zero or low field. These results point to a first-order field-induced metal-insulator transition. These findings can explain the complex phenomena observed near the phase boundary under a high magnetic field.
• Field-induced metal-insulator transition in partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

  A Kawamoto, M Yamasita, K Kumagai

  PHYSICAL REVIEW B 70 21 2004年12月 [査読有り][通常論文]
   

  A C-13-NMR study on nondeuterated and partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br is reported, where BEDT-TTF is bis(ethylenedithio)tetra-thiafulvalene. By using a BEDT-TTF molecule with C-13 as one of its central carbons, we could estimate the density of states from the Knight shift and the spin-lattice relaxation rate. Although the reduced mass effect predicted from the specific-heat measurement was not observed in the C-13-NMR spectrum, a metal-to-antiferromagnetic phase transition was observed with a phase separation at around 18 K on the half-deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br under a high magnetic field. No such transition occurred in the half-deuterated salt under a zero or low field. These results point to a first-order field-induced metal-insulator transition. These findings can explain the complex phenomena observed near the phase boundary under a high magnetic field.
• NMR studies on two-dimensional molecular conductors and superconductors: Mott transition in kappa-(BEDT-TTF)(2)X

  K Miyagawa, K Kanoda, A Kawamoto

  CHEMICAL REVIEWS 104 11 5635 - 5653 2004年11月 [査読有り][通常論文]
  
• Electron localization in the strongly correlated organic system κ-(BEDT-TTF)2X probed with nuclear magnetic resonance 13C-NMR

  Atsushi Kawamoto, Yosuke Honma, Ken-Ichi Kumagai

  Physical Review B - Condensed Matter and Materials Physics 70 6 1 - 60510 2004年08月 [査読有り][通常論文]
   

  κ-(BEDT-TTF)2X salts exhibit a wide range of properties from superconductivity to magnetic ordering. The phase diagram of this system has been understood as the competition between anti-ferromagnetic insulating behavior and superconductivity. The κ-(BEDT-TTF)2X system has been well explained using a parameter, U/W, as well as the high Tc cuprates. κ-(BEDT-TTF)2Cu2(CN)3, however, behaved as an insulator without magnetic ordering. This salt cannot be described by the phase diagram described by the competition between superconductivity and magnetism. It is interesting to explore the nature of this insulating phase with an eye toward understanding the universal phase diagram of the κ-(BEDT-TTF)2X system. Magnetic frustration due to the triangular spin lattice has recently been reported for κ-(BEDT-TTF) 2Cu2(CN)3 from 1H-nuclear magnetic resonance (NMR) study. To investigate the insulating properties of this salt, we characterized it using 13C-NMR. In contrast to previous 1H-NMR studies, at low temperatures, we observed line broadenings that were proportional to the hyperfine coupling constants, which suggested inhomogeous electron localization. We also observed antiferromagnetic fluctuations which, as is the case with other salts, intensified with decreasing temperature. To understand the electronic properties of κ-(BEDT-TTF) 2X system, in addition to the U/W, the electron localization effect from the relatively narrow bandwidth is important.
• Electron localization in the strongly correlated organic system kappa-(BEDT-TTF)(2)X probed with nuclear magnetic resonance C-13-NMR

  A Kawamoto, Y Honma, K Kumagai

  PHYSICAL REVIEW B 70 6 2004年08月 [査読有り][通常論文]
   

  kappa-(BEDT-TTF)(2)X salts exhibit a wide range of properties from superconductivity to magnetic ordering. The phase diagram of this system has been understood as the competition between anti-ferromagnetic insulating behavior and superconductivity. The kappa-(BEDT-TTF)(2)X system has been well explained using a parameter, U/W, as well as the high T-c cuprates. kappa-(BEDT-TTF)(2)Cu-2(CN)(3), however, behaved as an insulator without magnetic ordering. This salt cannot be described by the phase diagram described by the competition between superconductivity and magnetism. It is interesting to explore the nature of this insulating phase with an eye toward understanding the universal phase diagram of the kappa-(BEDT-TTF)(2)X system. Magnetic frustration due to the triangular spin lattice has recently been reported for kappa-(BEDT-TTF)(2)Cu-2(CN)(3) from H-1-nuclear magnetic resonance (NMR) study. To investigate the insulating properties of this salt, we characterized it using C-13-NMR. In contrast to previous H-1-NMR studies, at low temperatures, we observed line broadenings that were proportional to the hyperfine coupling constants, which suggested inhomogeous electron localization. We also observed antiferromagnetic fluctuations which, as is the case with other salts, intensified with decreasing temperature. To understand the electronic properties of kappa-(BEDT-TTF)(2)X system, in addition to the U/W, the electron localization effect from the relatively narrow bandwidth is important.
• Electron localization in the strongly correlated organic system kappa-(BEDT-TTF)(2)X probed with nuclear magnetic resonance C-13-NMR

  Kawamoto A, Honma Y, Kumagai K

  PHYSICAL REVIEW B 70 6 2004年08月 [査読有り][通常論文]
  
• C-13-NMR study on kappa-(BEDT-TTF)(2)X

  A Kawamoto, Y Honma, M Yamashita, J Sasaki, SI Okitsu, KI Kumagai

  JOURNAL DE PHYSIQUE IV 114 327 - 329 2004年04月 [査読有り][通常論文]
   

  kappa-(BEDT-TTF)(2)X salts show the variety physical properties from the Superconductivity to the magnetic ordering. It is important to investigate the characters of kappa-(BEDT-TTF)(2)X from microscopic probes, systematically. C-13-NMR is a one of the most powerful tool for this aim. In order to study the variety physical properties on of kappa-(BEDT-TTF)(2)X. We performed single crystal C-13-NMR works on deuterized samples, alloy system etc. Here-we report especially about kappa-(BEDT-TTF)(2)Cu-2(CN)(3) from our a several approaches in this proceedings. Recently, for kappa-(BEDT-TTF)(2)Cu-2(CN)(3), the magnetic frustrations are pointed Out. However, we found the evidence of the electron localization phenomenon on this salt from C-13-NMR work.
• Phase separation behaviour on kappa-(BEDT-TTF)(2) Cu[N(CN)(2)]Br

  S Okitsu, A Kawamoto, K Kumagai

  JOURNAL DE PHYSIQUE IV 114 357 - 359 2004年04月 [査読有り][通常論文]
   

  The system of the deuterated kappa-(BEDT-TTF-d[n,n])(2)Cu[N(CN)(2)]Br is situated in the critical region between the superconducting(SC) phase and the antiferromagnetic insulator (AFI) phase, and is just on the Mott type critical boundary of paramagnetic metal (PM) phase and paramagnetic insulator (PI) phase. We perform two single-crystal C-13-NMR studies on the non and the fully deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br at low temperature with the applied field 9.4T. We found two new experimental results. One is that the phase separation is found in kappa-(BEDT-TTF-d[0,0])(2)Cu[N(CN)(2)]Br salt, like partially deuterated kappa-(BEDT-TTF)(2) Cu[N(CN)(2)]Br salt. The other is that the phase separation is observed at around T* with the applied field parallel to the conducting layer, unlike partially deuterated kappa-(BEDT-TTF-d[n,n])(2) Cu[N(CN)(2)]Br. The former result suggests the field induces AF transition. the latter result suggests there is the field direction dependence of the M-I phase separation behavior in kappa-(BEDT-TTF-d[4,4])(2) Cu[N(CN)(2)]Br.
• Charge disproportionate state of BEDT-TTF beta '' -salts

  T Yamamoto, M Uruichi, K Yakushi, J Yamaura, H Tajima, A Kawamoto

  JOURNAL DE PHYSIQUE IV 114 397 - 399 2004年04月 [査読有り][通常論文]
   

  We studied C=C stretching bands of beta" (ET)(3)(ReO4)(2) and beta" (ET)(4)M(CN)(4)H2O (M=Pt, Pd and Ni) at the low temperatures below 300 K in order to verify the inhomogeneous charge distributions. A drastic spectral change was observed for beta- (ET)(3)(ReO4), at 80 K, below which the system falls into the charge ordered state. On the other hand, a continuous spectral change was observed for beta''-(ET)(4)Ni(CN)(4)H2O and beta"-(ET)(4)Pd(CN)(4)H2O. v(2) for M=Ni and Pd exhibited a doublet, suggesting an inhomogeneous charge distributions. v(2) for M=Pt did not show a peak splitting, while C=C bands for the deuterium analogue exhibited a behaviour similar to those for M=Ni.
• High-pressure Raman study of the charge ordering in α-(BEDT-TTF)2I3

  Roman Wojciechowski, Kaoru Yamamoto, Kyuya Yakushi, Makoto Inokuchi, Atsushi Kawamoto

  PHYSICAL REVIEW B 67 22 224105  2003年06月16日 [査読有り][通常論文]
   

  Charge distributions in the donor layer for the paramagnetic semimetal-like and nonmagnetic insulating phases of the α − (BEDT − TTF)2I3 single crystal [BEDT-TTF:?bis(ethylenedithiolo)tetrathiafulvalene] were investigated under quasihydrostatic pressures up to 3.6 GPa using Raman spectroscopy. The results confirmed the appearance of charge disproportionation below the metal-insulator phase transition temperature (TMI). The average charge-disproportionation ratio, 0.2?0.8, at ambient pressure was quite pressure sensitive and decreased by ca. 0.1e/GPa with increasing pressure. This result is ascribed to the faster increase of the transfer integrals than the intersite Coulomb repulsions under pressure. The loss of the inversion centers in the nonmagnetic insulating phase, concluded by the selection rule, suggests that the charge is ordered such that it forms a so-called horizontal stripe. Nonuniform charge distributions were also found at temperatures above TMI for the paramagnetic semimetal-like phase. The experimentally determined small charge difference among BEDT-TTF at crystallographically nonequivalent sites is consistent with the band calculations. ? 2003 The American Physical Society.
• Field-induced superconductor-insulator transition in layered organics

  H Taniguchi, A Kawamoto, K Kanoda

  PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 388 597 - 598 2003年05月 [査読有り][通常論文]
   

  A partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br salt, which is a superconductor situated near the Mott insulator, has been investigated by resistivity measurements under magnetic fields. The superconducting transition of this salt is replaced by the first-order metal-insulator transition by magnetic field. This field-induced transition fades away when the sample cooling around 80 K is slowed down. The present findings lead us to bring to mind possible realization of the ideal electric switch controllable with the magnetic field. (C) 2003 Elsevier Science B.V. All rights reserved.
• Phase diagram of partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

  N Matsunaga, K Yamashita, M Yamashita, A Kawamoto, K Nomura

  PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 388 591 - 592 2003年05月 [査読有り][通常論文]
   

  The phase diagram of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br around the metal-insulator (MI) boundary controlled by partially deuteration and by cooling rate through the 80 K anomaly has been investigated by resistivity measurements under magnetic fields. The humps of resistance were observed at 33.5 K corresponding to the T* anomaly and at 9.5 K with the hysteresis of resistance in the partially deuterated sample for slowly cooled. According to approach to the critical region of MI transition from the metallic side by the increase of cooling rate: (a) the hump of resistance at the T* anomaly is shifted towards a lower temperature and (b) the temperature of the resistance hump with the hysteresis increases. Our results suggest that these anomalies are related to the phase separation of the metallic and insulator phase around the MI boundary. (C) 2003 Elsevier Science B.V. All rights reserved.
• STM spectroscopy on partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

  K Ichimura, K Suzuki, K Nomura, A Kawamoto

  SYNTHETIC METALS 137 1-3 1229 - 1230 2003年04月 [査読有り][通常論文]
   

  We report the electron tunneling spectroscopy on kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br using a low temperature STM. Protonated d[0,0] and partially deuterated d[2,2] salts were studied.. In both salts, the functional shape of the tunneling differential conductance curve in the superconducting state is explained by the d-wave pairing symmetry. We obtain the gap parameter Delta as 2.1-3.9 and 3.0-4.8 meV for d[0,01 and d[2,21 salt, respectively. The value of 2Delta/kT(c) in d[2,2] salt is slightly larger than that in d[0,0] salt. The pseudogap is observed below about 50 K in both salts.
• Magnetic properties of the alloy of kappa-(BEDT-TTF)(2(1-X))(BEDSe-TTF)(2X)Cu[N(CN)(2)]Br

  J Sasaki, A Kawamoto, K Kumagai

  SYNTHETIC METALS 137 1-3 1249 - 1250 2003年04月 [査読有り][通常論文]
   

  In kappa-(BEDT-TTF)(2)X, the relationship between the AF-fluctuation and the superconductivity has been discussed by many researchers. In order to investigate the mechanism of the superconductivity in kappa-(BEDT-TTF)(2)X, we prepared the alloy of kappa-(BEDT-TTF)(2(1-X))(BEDSe-TTF)(2X)Cu[N(CN)(2)]Br and measured the magnetic properties of the alloy. The increase of X shifted T, lower and the superconductivity was suppressed over X=0.33. To check the magnetic fluctuation, we also measured the spin lattice relaxation rate (T1T)(-1) of the series of the alloy system.
• C-13-NMR study on partially deuterized kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

  A Kawamoto, M Yamashita, K Kumagai

  SYNTHETIC METALS 137 1-3 1303 - 1304 2003年04月 [査読有り][通常論文]
   

  Using partially deuterized BEDT-TTF molecules, we performed C-13-NMR study of a series of partially deuterized K(BEDT-TTF)(2)Cu[N(CN)(2)]Br salts, where BEDT-TTF is bis-(ethylenedithio)tetrathiafulvalene. We synthesized partially deuterized BEDT-TTF molecules C-13-enriched on only one side of the central carbon sites. The substitution of one side of the central carbon avoid the Pake doublet and we can estimate the density of states from the Knight-shift and the spin-lattice relaxation rate. The reduced mass effect predicted from the specific heat measurement near the SC-AFI boundary was not observed in the C-13-NMR measurement but the phase separation behavior was observed.
• Raman study of charge disproportionation in alpha-(BEDT-TTF)(2)I-3

  R Wojciechowski, K Yamamoto, K Yakushi, A Kawamoto

  SYNTHETIC METALS 135 1-3 587 - 588 2003年04月 [査読有り][通常論文]
   

  Raman studies of alpha-(BEDT-TTF)(2)I-3 [BEDT-TTF is bis-ethylenedithiolo(tetrathiafulvalene)] have been performed to investigate the charge distribution between BEDT-TTFs below and above the metal-insulator phase transition at T-M.(I)=135 K. Following the crystal-symmetry lowering at T-M.(I), clear +/-0.3e deviation from average 0.5e charge has been found in the nonmagnetic insulating phase. In the paramagnetic semi-metal-like phase, the split of one of the Raman active mode suggests charge nonequivalence between donors.
• Site-selective NMR study of neutral-ionic transition in (BEDT-TTF)(Cl,MeTCNQ)

  K Miyagawa, K Kanoda, A Kawamoto, T Hasegawa

  SYNTHETIC METALS 135 1-3 619 - 620 2003年04月 [査読有り][通常論文]
   

  The title compound undergoes a neutral-ionic (N-I) phase transition under pressure. In order to examine the electronic state of BEDT-TTF and ClMeTCNQ molecules separately by NMR,we prepared the complex with Cl,MeTCNQ and C-13, deuterium-substituted BEDT TTF molecules. The C-13 and H-1 NMR measurements were performed at ambient and applied pressures. Under 8 kbar, the N-I transition was found to be continuous. We also found that the I-phase is nonmagnetic state.
• Phase control of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br by partial deuteration

  A Kawamoto, M Yamashita, K Kumagai, H Taniguchi, Y Nakazawa, K Miyagawa, K Kanoda

  SYNTHETIC METALS 133 123 - 124 2003年03月 [査読有り][通常論文]
   

  kappa-(BEDT-TTF)(2)X system is well known as the strong correlated electron system with the phase boundary of the superconducting and the antiferromagnetic ordering phases. We controlled the boundary with the partial deuterization technique on kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br and found the boundary was sensitive to cooling rate around at 80 K, at which the lattice anomaly occurred. We also found the external magnetic field dependence of the boundary. (C) 2002 Elsevier Science B.V. All rights reserved.
• C-13 NMR study of partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

  M Yamashita, A Kawamoto, K Kumagai

  SYNTHETIC METALS 133 125 - 127 2003年03月 [査読有り][通常論文]
   

  Synthesis of deuterated and C-13-enriched BEDT-TTF, and the results of C-13 NMR (nuclear magnetic resonance) measurement of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br salt are reported where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene. We synthesized the BEDT-TTF molecule 13 C-enriched on only one side of the central carbon sites. By using this molecule, we could avoid the Pake doublet and estimate the density of states from the Knight-shift and the spin-lattice relaxation rate. The reduced mass effect predicted from the specific heat measurement was not observed in the C-13 NMR measurement. (C) 2002 Elsevier Science B.V. All rights reserved.
• Tunneling spectroscopy on kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br using STM

  K Ichimura, K Suzuki, K Nomura, A Kawamoto

  SYNTHETIC METALS 133 213 - 214 2003年03月 [査読有り][通常論文]
   

  We report the electron tunneling spectroscopy on kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br using a low temperature STM. In the superconducting state, tunneling spectra show the energy gap structure clearly. The tunneling differential conductance shows linear dependence on energy inside the gap edge. The conductance curve is well fitted by the d-wave calculation with a little broadening. The d-wave gap parameter is obtained as Delta(0) = 2.5-3.5 meV, correspondingly, 2Delta(0)/kT(c) = 5.0-7.1. The pairing symmetry is consistent with that in kappa-(BEDT-TTF)(2)Cu(NCS)(2) as well as the gap parameter. The broad dip structure around the Fermi level is found in tunneling spectra above T-c. The pseudogap structure is observed below 50 K. (C) 2002 Elsevier Science B.V. All rights reserved.
• Vibrational spectra of BEDT-TTF based 2D charge ordering systems

  K Yamamoto, K Yakushi, K Miyagawa, K Kanoda, A Kawamoto, J Yamaura, T Enoki

  SYNTHETIC METALS 133 269 - 272 2003年03月 [査読有り][通常論文]
   

  We measured the polarized Raman spectra of theta-(BEDT-TTF)(2)RbZn(SCN)(4) (RbZn) and (BEDT-TTF)(3)CuBr4 (CuBr) to investigate the detailed property of charge ordering (CO), and discussed an approach for analyzing the vibrational spectra of CO systems. The Raman spectra of the two compounds showed multiple peaks around the C=C stretching region. With the help of isotope-shift measurements, the multiple peaks of RbZn were assigned to two symmetric C=C stretching modes, called v(2) and v(3). We used the vibronic signals of v(3) to characterize the spatial symmetry of charge distribution, and employed the peak frequencies of v, with weaker vibronic coupling effect to the estimation of charge disproportionation ratio. Similar spectral analysis was applied to CuBr salt to verify whether the approach can be applied to other systems. (C) 2002 Elsevier Science B.V. All rights reserved.
• Field switching of superconductor-insulator bistability in artificially tuned organics

  H. Taniguchi, K. Kanoda, A. Kawamoto

  Physical Review B - Condensed Matter and Materials Physics 67 1 2003年01月14日 [査読有り][通常論文]
   

  Layered organic superconductors situated in the vicinity of a superconductor-insulator (SI) phase boundary show switching between the SI bistable states by application of magnetic field. First, we show that an electronic phase of (formula presented) [BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene] can be finely tuned so as to approach the SI boundary by combination of chemical modification of the BEDT-TTF molecules and regulation of cooling rate. Then, we demonstrate that the superconducting phase tuned in this way undergoes a field-induced first-order transition into the insulating phase. © 2003 The American Physical Society.
• Proximity of pseudogapped superconductor and commensurate antiferromagnet in a quasi-two-dimensional organic system

  K Miyagawa, A Kawamoto, K Kanoda

  PHYSICAL REVIEW LETTERS 89 1 2002年07月 [査読有り][通常論文]
   

  We performed the single-crystal C-13 NMR studies on a quasi-two-dimensional system, deuterated kappa-(BEDT- TTF)(2)Cu[N (CN)(2)]Br , which is just on the border of the Mott transition. The NMR spectra are separated into two parts coming from the metallic (superconducting) and insulating phases due to the phase separation at low temperature. The examination of the separated spectra revealed that the Mott transition in this system is characterized by the first-order transition between the pseudogapped superconductor and the simplest commensurate antiferromagnet with a moment of 0.26mu(B)/dimer .
• Charge ordering in theta-(BEDT-TTF)(2)RbZn(SCN)(4) studied by vibrational spectroscopy

  K Yamamoto, K Yakushi, K Miyagawa, K Kanoda, A Kawamoto

  PHYSICAL REVIEW B 65 8 2002年02月 [査読有り][通常論文]
   

  Charge distribution in the insulating phase of theta-(BEDT-TTF)(2)RbZn(SCN)(4) [BEDT-TTF denotes bis(ethylenedithiolo)tetrathiafulvalene] is investigated using the polarized Raman and infrared (IR) spectroscopy. Both of the Raman and IR spectra showed a multiple-peaks pattern below metal-insulator transition temperature. We assigned the carbon-double-bond (C=C) stretching-modes based on the isotope shift in the C-13-substituted sample, and performed a factor-group analysis for the polarized IR and Raman spectra. These results proved that charge disproportionation (CD) takes place in the insulating phase, and that the spatial pattern of the charge ordering agrees with the symmetry determined by the x-ray diffraction. The CD ratio was estimated from the frequency of a ring C=C stretching mode that is weakly coupled with electronic excited states. A systematic way to investigate the CD phenomenon based on vibrational spectroscopy is discussed.
• Band-selective NMR of a pi-d hybridized electronic system

  A Kawamoto, K Miyagawa, K Kanoda

  MOLECULAR CRYSTALS AND LIQUID CRYSTALS 379 95 - 100 2002年 [査読有り][通常論文]
   

  A pi-d hybrid electronic system, (DMe-DCNQI)(2)Cu, where the pi orbital of the organic molecule, DMe-DCNQI, is strongly hybridized with the d(xy) orbital of Cu, has been studied by N-15 and C-13 NMR at three sites. The analysis of Knight shift, K, local Spill susceptibilities in the pi and d orbitals were determined separately. The pi and d spin susceptibilities were found to be quite different in magnitude and temperature dependence. Moreover, the Knight shift was separated into those of two constituent bands; a one-dimensional pi band and a three-dimensional pi-d band. The relative weight of the band susceptibilities is strongly temperature-dependent.
• The C=C stretching vibrations of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br and its isotope analogues

  M Maksimuk, K Yakushi, H Taniguchi, K Kanoda, A Kawamoto

  JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 12 3728 - 3738 2001年12月 [査読有り][通常論文]
   

  The C=C stretching modes in resonance Raman spectra and infrared reflectivity were measured at temperatures between 15 K and 300 K using various polarizations in kappa-(BEDT TTF)(2)Cu[N(CN)(2)]Br, its fully and partially deuterated analogues, and C-13-substituted analogue. The infrared- and Raman-active bands were re-assigned based on the factor group analysis. We found a Raman-active EMV-coupled nu (3) mode near 1420 cm(-1), which shows a large downshift and broadening through the inter-dimer EMV interaction. The mixing of the bridge and ring C=C stretching vibrations depend upon the symmetry of the crystal mode. In contrast to deuterated crystals, the non-deuterated crystals show a splitting in the nu (2), nu (3), and nu (27) bands.
• Ferromagnetic and antiferromagnetic fluctuations of pi-d itinerant electrons disclosed by band-selective NMR

  A Kawamoto, K Miyagawa, K Kanoda

  PHYSICAL REVIEW LETTERS 87 10 2001年09月 [査読有り][通常論文]
   

  We present a band-selective NMR method to probe the constituent electronic bands separately in the condensed molecular matter. This method is applied to an organic-inorganic pi -d hybrid metal, and its utility to give the static and dynamic spin susceptibilities for the constituent bands is demonstrated. The analysis of the results uncovers an exotic feature; the antiferromagnetic and ferromagnetic correlations are enhanced in separate bands in a single material. This finding provides a novel scope connecting the metal-insulator transitions in this system and the manganese oxides.
• Thermodynamic studies of electron correlation effects on organic salts based on BEDT-TTF and DCNQI molecules

  Y Nakazawa, H Taniguchi, A Kawamoto, K Miyagawa, K Hiraki, K Kanoda

  JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 62 1-2 385 - 388 2001年01月 [査読有り][通常論文]
   

  A thermodynamic investigation on the electronic properties of several organic salts based o \ hskip24pt \ hbox{(1)}n BEDT-TTF and DCNQI molecules is performed by means of high-precision specific-heat measurements in the temperature range between 0.9 and 6 K. The electronic specific-heat coefficient gamma for dimeric insulators is almost 0 mJ/mol K-2, which is explained by the picture of Mott-Hubbard gap in the effectively half-filled band. The non-dimeric salt of (DI-DCNQI)(2)Ag, on the other hand, shows an unexpectedly large gamma value of about 30-40 mJ mol(-1) K-2 representing the existence of large low-energy excitations from the charge-ordered insulating ground state. The difference of the low-temperature electronic specific-heat behavior between the dimeric and non-dimeric systems demonstrates that manifestation of electron correlation effects is qualitatively different in these systems. (C) 2000 Elsevier Science Ltd. All rights reserved.
• Charge ordering in a quasi-two-dimensional organic conductor

  K. Miyagawa, A. Kawamoto, K. Kanoda, K. Kanoda

  Physical Review B - Condensed Matter and Materials Physics 62 12 R7679 - R7682 2000年09月15日 [査読有り][通常論文]
   

  The first nuclear magnetic resonance (NMR) evidence of charge ordering in a quasi-two-dimensional organic conductor is presented. We have performed 13C NMR shift and relaxation rate measurements for the organic conductor, θ-(BEDT-TTF)2RbZn(SCN)4, with a quasi-two-dimensional quarter-filled band. Below the metal-insulator transition at 195 K, the NMR spectrum splits into two kinds of lines. The spin shifts and relaxation rates are quite different between the two lines, showing charge disproportionation of 1:6: This result demonstrates a route to the correlation-induced insulator transition in organic conductors.
• Charge ordering in a quasi-two dimensional organic conductor

  K Miyagawa, A Kawamoto, K Kanoda

  PHYSICAL REVIEW B 62 12 R7679 - R7682 2000年09月 [査読有り][通常論文]
   

  The first nuclear magnetic resonance (NMR) evidence of charge ordering in a quasi-two-dimensional organic conductor is presented. We have performed C-13 NMR shift and relaxation rate measurements for the organic conductor, theta-(BEDT-TTF)(2)RbZn(SCN)(4), with a quasi-two-dimensional quarter-filled band. Below the metal-insulator transition at 195 K, the NMR spectrum splits into two kinds of lines. The spin shifts and relaxation rates are quite different between the two lines, showing charge disproportionation of 1:6. This result demonstrates a route to the correlation-induced insulator transition in organic conductors.
• Phase control of strongly correlated organic conductor

  H Taniguchi, A Kawamoto, K Kanoda

  PHYSICA B 284 519 - 520 2000年07月 [査読有り][通常論文]
   

  The kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br salts were synthesized from nondeuterated, partially, and fully deuterated BEDT-TTF molecules. The electrical resistance of these salts was examined systematically as functions of temperature and cooling rate, and found to change from metallic to insulating behaviors by the progressive deuterations and increasing the cooling rate. This means the active control of. the correlation effect of electrons in this family. (C) 2000 Elsevier Science B.V. All rights reserved.
• Commensurate magnetic structure in kappa-(BEDT-TTF)(2)X

  K Miyagawa, A Kawamoto, K Uchida, K Kanoda

  PHYSICA B 284 1589 - 1590 2000年07月 [査読有り][通常論文]
   

  The kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br is a quasi-two-dimensional superconductor with the highest T-c of similar to 12 K among organic conductors. However, the antiferromagnetic insulating state appears by deuteration of BEDT-TTF (kappa-d8-Br) or substitution of Cl (kappa-Cl) for Br. The C-13 NMR measurements of these two insulating compounds, which are situated near the superconducting phase, were carried out to probe magnetic structure. The NMR spectra of kappa-Cl and kappa-d8-Br clearly indicate the commensurate antiferromagnetic structure with ordered moments of 0.45 mu(B)/(BEDT-TTF), and 0.3 mu B/(BEDT-TTF)(2), respectively, which provides unambiguous evidence that kappa-Cl and kappa-d8-Br are Mott insulators. (C) 2000 Elsevier Science B.V. All rights reserved.
• Electronic specific heat at the boundary region of the metal-insulator transition in the two-dimensional electronic system of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

  Nakazawa Y, Taniguchi H, Kawamoto A, Kanoda K

  PHYSICAL REVIEW B 61 24 R16295 - R16298 2000年06月15日 [査読有り][通常論文]
  
• C-13 NMR study of an organic conductor, theta-(BEDT-TTF)(2)RbZn(SCN)(4)

  K Miyagawa, A Kawamoto, K Kanoda

  PHYSICA B 281 680 - 681 2000年06月 [査読有り][通常論文]
   

  The compound mentioned in the title is a quasi-two-dimensional organic conductor exhibits a mental-insulator transition accompanied by structural modification at T-M1 similar to 190 K. while the tight-binding band calculation suggests a 3/4 filled band at higher temperatures. The C-13 NMR measurements have been performed on a single crystal to clarify the electronic nature of the metal-insulator transition. At room temperature. the C-13 NMR spectrum indicates that all BEDT-TTf molecules are electronically equivalent. Below T-M1. however. it splits into two kinds of spectra with different Knight shifts and spin-lattice relaxation rates. These results show that change disproportionation occurs below T-M1 and that long-range Coulomb interaction is important in this system. (C) 2000 Elsevier Science B.V. All rights reserved.
• Orbital- and band-dependent susceptibility in a pi-d hybrid electronic system, (DMe-DCNQI)(2)Cu

  A Kawamoto, K Miyagawa, K Kanoda

  PHYSICA B-CONDENSED MATTER 281 677 - 679 2000年06月 [査読有り][通常論文]
   

  A pi-d hybrid electronic system, (DMe-DCNQI)2Cu, where the pi orbital of the organic molecule, DMe-DCNQI, is strongly hybridized with the d(xy) orbital of Cu, has been studied by (15)N and (13)C NMR at three sites. The analysis of Knight shift, K, and local spin susceptibilities in the pi and d orbitals was carried out separately. The pi and d spin susceptibilities were found to be quite different in magnitude and temperature dependence. Moreover, the Knight shift was separated into those of two constituent bands; a one-dimensional pi: band and a three-dimensional pi-d band. The relative weight of the band susceptibilities is strongly temperature dependent. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
• Electronic specific heat of BEDT-TTF-based organic conductors

  Y Nakazawa, H Taniguchi, A Kawamoto, K Kanoda

  PHYSICA B 281 899 - 900 2000年06月 [査読有り][通常論文]
   

  Thermodynamic studies for a series of partially deuterated kappa-(BEDT-TTF)(2) Cu[N(CN)(2)]Br single crystals were performed in order to see variation of the normal-state density of sates around the two-dimensional Mott transition caused by the bandwidth control. The electronic specific heat coefficient gamma was found to decrease monotonously when the system approaches the boundary from the metallic region. The Brinkman-Rice-type mass enhancement is absent near the critical boundary. (C) 2000 Elsevier Science B.V. All rights reserved.
• Electronic specific heat at the boundary region of the metal-insulator transition in the two-dimensional electronic system

  Y. Nakazawa, H. Taniguchi, A. Kawamoto, K. Kanoda

  Physical Review B - Condensed Matter and Materials Physics 61 24 R16295 - R16298 2000年 [査読有り][通常論文]
   

  The electronic specific heat of partially deuterated organic conductors (Formula presented) [where BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene], which are situated around the critical boundary of a metal-insulator transition in two dimensions, are studied. It was found that when the system has access to the (Formula presented) boundary with the progressive deuteration of BEDT-TTF molecules, the normal-state γ term diminishes. The absence of mass enhancement is marked as a basis for the future study of electronic features related to the nature of superconductivity and also on the universality and variation of a possible Mott transition in two-dimensional systems. © 2000 The American Physical Society.
• pi-d orbital hybridization in the metallic state of organic-inorganic complexes seen by C-13 and N-15 NMR at selective sites

  K Miyagawa, A Kawamoto, K Kanoda

  PHYSICAL REVIEW B 60 21 14847 - 14851 1999年12月 [査読有り][通常論文]
   

  An organic pi-inorganic d hybrid electronic system, (DMe-DCNQI)(2)Cu, was investigated through N-15 and C-13 NMR at three sites. The analysis of the Knight shift uncovered local spin susceptibilities in the DCNQI pi and Cu d orbitals separately. The spin susceptibility was found to be orbital dependent. The pi spin susceptibility dominates the d spin susceptibility in magnitude. However, the latter grows significantly at low temperatures while the former is temperature insensitive. This demonstrates temperature-dependent interplay between the pi and d orbitals and gives insight into the anomalous metal-insulator transition under pressure or deuteration. [S0163-1829(99)03945-4].
• Charge ordering in organic conductors

  K Kanoda, K Miyagawa, A Kawamoto, K Hiraki

  JOURNAL DE PHYSIQUE IV 9 P10 353 - 355 1999年12月 [査読有り][通常論文]
   

  The charge ordering phenomena in the organic conductors, (R(1),R(2)-DCNQI)(2)M, have been studied by (13)C and (15)N NMR spectroscopy. The pi electron ordering in (I,I-DCNQI)(2)Ag and Cu d electron ordering in (CD(3),CD(3)-DCNQI)(2)Cu, which are evidenced by splitting of the NMR line, show quite different behaviors in the charge profile and the order of the transition, reflecting the different driving forces. The analysis of Knight shifts revealed that the pi spin susceptibility dominates the d spin susceptibility in the pi-d hybridized metallic state.
• pi-d orbital hybridization in the metallic state of organic-inorganic complexes seen by C-13 and N-15 NMR at selective sites

  Miyagawa K, Kawamoto A, Kanoda K

  PHYSICAL REVIEW B 60 21 14847 - 14851 1999年12月01日 [査読有り][通常論文]
  
• Metal-insulator transition in partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

  H Taniguchi, A Kawamoto, Y Nakazawa, K Kanoda

  SYNTHETIC METALS 103 1-3 2250 - 2250 1999年06月 [査読有り][通常論文]
   

  The kappa-(BEDT-TTF)(2)Cu[N(CN)2]Br salts were synthesized from non-, partially, and fully deuterated BEDT-TTF molecules. The electrical resistivities of this family have been studied. The resistive state is progressively changed from metallic to insulating behaviors by the partial deuterations. The kink of the resistive curve with hysteresis was observed around 78K irrespectively of the degree of the deuteration.
• Two types of charge ordering in DCNQI-metal complexes studied by C-13-NMR

  K Kanoda, K Miyagawa, A Kawamoto, K Hiraki

  SYNTHETIC METALS 103 1-3 1825 - 1826 1999年06月 [査読有り][通常論文]
   

  The pi electron charge ordering in (DI-DCNQI)(2)Ag with a 1/4-filled 1-d band and the d electron charge ordering in deuterated (DMe-DCNQI)(2)Cu with the pi-d hybridization have been characterized by C-13 NMR. The profile of the ordering is quite different between the two systems, reflecting the different driving force. The intersite Coulomb interaction between the pi-electrons is considered to be crucial in the former case while the perfect charge ordering found in the latter salt seems to invoke cooperative mechanism including the rr electron-lattice (Peierls) instability, dxy level-lattice instability and strong correlation in the Cu site.
• Superconductor-insulator phase transformation of partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br by control of the cooling rate

  H Taniguchi, A Kawamoto, K Kanoda

  PHYSICAL REVIEW B 59 13 8424 - 8427 1999年04月 [査読有り][通常論文]
   

  The electronic state of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br is precisely controlled around the superconductor-insulator boundary by partial deuteration. As the salt approaches the boundary with progressive deuteration, the cooling rate influences the electronic state strongly; the low-temperature metallic phase is transformed into the insulating phase with collapse of the bull; superconductivity by the rapid cooling. This phenomenon is discussed in terms of the change in U/W and the possible effect of the disorder on the metallic (superconducting) phase near the Mott insulator, where U and W are the intradimer Coulomb repulsion and the bandwidth. [S0163-1829(99)01114-5].
• Superconductor-insulator phase transformation of partially deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br by control of the cooling rate

  H. Taniguchi, A. Kawamoto, K. Kanoda

  Physical Review B 59 13 8424 - 8427 1999年 [査読無し][通常論文]
  
• Superconductor-insulator transition controlled by partial deuteration in BEDT-TTF salt

  A Kawamoto, H Taniguchi, K Kanoda

  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 120 42 10984 - 10985 1998年10月 [査読有り][通常論文]
  
• C-13 NMR study of the metal-insulator transition in (DMe-DCNQI)(2)Cu systems with partial deuteration

  A Kawamoto, K Miyagawa, K Kanoda

  PHYSICAL REVIEW B 58 3 1243 - 1251 1998年07月 [査読有り][通常論文]
   

  The electronic states of-a series of (DMe-DCNQI)(2)Cu systems with nondeuterated and partially deuterated methyl groups in a DMe-DCNQI molecule have been investigated.by C-13 NMR measurements at the cyano carbon sites. The Knight shift of the nondeuterated specimen, which is metallic in the;whole temperature range, is not scaled-to the total spin susceptibility, demonstrating that the metallic state has several electronic bands with different local spin susceptibility due to the pi-d hybridization. In the insulating phases of the partially deuterated specimens, C-13 NMR spectra are split into two lines, one of which has a nearly zero shift and the other has a large positive shift with the Curie-Weiss temperature dependence. The former line comes from the cyano group coordinated to the nonmagnetic Cu+ ion, while the latter comes from the cyano group coordinated to the magnetic Cu2+ ion. The-sign of the shift and intensity analysis provide an evidence that, in the insulating phase, spin is localized exclusively at one-third of the Cu sites without any population on the DCNQI molecule. This is considered as a manifestation of strong electron correlation in the Cu sites. The low-temperature reentrant metallic state in the partially deuterated system is found to.be just the same as the stable metallic state in the nondeuterated system through the shift and relaxation rate behaviors. No fluctuations are observed,in the vicinity of the metal-insulator and insulator-metal reentrant transitions, showing that the transitions are of the first order. [S0163-1829(98)01628-2].
• C-13 NMR study of nesting instability in alpha-(BEDT-TTF)(2)RbHg(SCN)(4)

  K Miyagawa, A Kawamoto, K Kanoda

  PHYSICAL REVIEW B 56 14 R8487 - R8490 1997年10月 [査読有り][通常論文]
   

  The low-temperature nesting instability in the quasi-two-dimensional organic conductor, alpha-(BEDT-TTF)(2)RbHg(SCN)(4), has been investigated by C-13 NMR. Below 12 K, drastic decreases in the Knight shift and 1/(T1T) were observed with neither splitting nor broadening in the NMR spectra. The 1/(T1T) shows no enhancement around the nesting instability, unlike the conventional spin-density-wave (SDW) transition. The present C-13 NMR data are suggestive of nonmagnetic transition but allow only an unusual case of mobile state in the SDW scenario.
• C-13 and H-1 NMR study of vortex dynamics in a layered organic superconductor at selective nuclear sites

  K Kanoda, K Miyagawa, A Kawamoto

  PHYSICA C 282 2063 - 2064 1997年08月 [査読有り][通常論文]
   

  The quasi-two-dimensional superconductor, kappa-(BEDT-TTF)(2)Cu(NCS)(2), under a perpendicular field was investigated by NMR relaxation rate measurements at the three different nuclear sites. The vortex dynamics contribution to the relaxation rate was separated from the quasiparticle contribution and found to show a peak formation around 2 K with a site-dependent peak height. The analysis supports that the peak behavior does not come from the simple crossover but from some qualitative change in the vortex dynamics.
• Deuterated kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br: A system on the border of the superconductor-magnetic-insulator transition

  A Kawamoto, K Miyagawa, K Kanoda

  PHYSICAL REVIEW B 55 21 14140 - 14143 1997年06月 [査読有り][通常論文]
   

  The electronic state of the deuterated salt of the organic system kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, has been investigated by dc/ac susceptibility and H-1/C-13 NMR measurements. We found that the system is situated in the critical region of the transition between a superconducting phase with a T-C of similar to 11.5 K and an antiferromagnetic phase with a T-N of 14-15 K. It was also found that the rapid cooling through 80 K drives the superconducting phase into the magnetic phase, that is discussed in the light of the role of disorder near the Mott transition.
• C-13-NMR study on beta-(BEDT-TTF)(2)I-3

  K Miyagawa, A Kawamoto, K Kanoda

  SYNTHETIC METALS 85 1-3 1537 - 1538 1997年02月 [査読有り][通常論文]
   

  The C-13-NMR and spin susceptibility measurements were performed to investigate the electronic state in beta-(BEDT-TTF)(2)I-3 before and during annealing. Interrelation between incommensurate superlattice, low temperature electronic anomaly, superconducting transition temperature and density of states in this salt was found.
• C-13-NMR study of Mott insulating phase in kappa-(BEDT-TTF)(2)X family

  A Kawamoto, K Miyagawa, H Taniguchi, K Kanoda

  SYNTHETIC METALS 85 1-3 1547 - 1548 1997年02月 [査読有り][通常論文]
   

  The kappa-(BEDT-TTF)(2)X family are quite attractive in the study of metal-insulator transitions and competition between superconductivity and magnetic ordering. We report C-13-NMR study of X = Cu[N(CN)(2)]Cl salt and discuss on the electronic structure, compared with the results of superconducting salts. In addition, we found that the deuterated Cu[N(CN)(2)]Br salt, when cooled rapidly, showes AF ordering like the Cu[N(CN)(2)]Cl salt with only minor fraction of superconducting phase. We also report C-13-NMR study of this salt.
• NMR study of superconductivity in kappa-(BEDT-TTF)(2)X

  K Miyagawa, A Kawamoto, K Kanoda

  SYNTHETIC METALS 85 1-3 1545 - 1546 1997年02月 [査読有り][通常論文]
   

  The electron pairing symmetry in the superconductivity in kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, a typical superconductor in a family of kappa-(BEDT-TTF)(2)X, has been investigated by C-13 and H-1 NMR measurements. The C-13 nuclear spin-lattice relaxation rate, T-13(1)-1, in a field parallel to the conducting layers shows an abrupt decrease below the transition temperature. There is no sign of the Hebel-Slichter coherence peak expected in the conventional superconductivity. Analyzing H-1 NMR relaxation rate, which probes the vortex dynamics preferentially, we succeeded in separating the measured T-13(1)-1 into the vortex-dynamics contribution and the quasi-particle contribution. The latter is found to follow a T-3-law, that is consistent with unconventional superconductivity with line nodes in gap parameter. The NMR measurements at the two nuclear sites with different hyperfine couplings within a molecule provide a useful method to extract nuclear relaxation due to quasi-particles.
• N-15 and C-13 NMR study of (DMe-DCNQI)(2)Cu

  A Kawamoto, K Miyagawa, K Kanoda

  SYNTHETIC METALS 86 1-3 2083 - 2084 1997年02月 [査読有り][通常論文]
   

  In order to investigate the electronic state of the metallic (DMe-DCNQI)(2)Cu, we prepared isotope-enriched DMe-DCNQI molecules where each site of =N-CN was substituted by C-13 and N-15 and performed C-13 and N-15-NMR measurements. Using the spectra of (DMe-DCNQI)(2)LI with no magnetic contribution from metal ion as reference, we succeeded in separating the two contributions to the Knight shift; the DCNQI pi part and the Cu ion part, which could be probed through the coordinated N atom.
• NMR study of (BEDT-TTF)(TCNQ) at selective nuclear sites

  A Kawamoto, K Miyagawa, A Shimizu, K Kanoda

  SYNTHETIC METALS 85 1-3 1601 - 1602 1997年02月 [査読有り][通常論文]
   

  The charge transfer complex, (BEDT-TTF)(TCNQ), is a hybrid system which consists of one-dimensional (1D) columns and two-dimensional (2D) BEDT-TTF layers and is known to be a paramagnetic insulator below room temperature. In order to examine the electronic structures of 1D and 2D layers separately, we prepared the complex between TCNQ and C-13, deuterium-substitured BEDT-TTF. We report the site-selective NMR study on this sample and discuss the electronic structure of the 1D and 2D electronic subsystems.
• Nesting instability in a family of alpha-(BEDT-TTF)(2)MHg(SCN)(4) [M=K, Rb, NH4] studied by C-13-NMR

  K Miyagawa, A Kawamoto, K Kanoda

  SYNTHETIC METALS 86 1-3 1987 - 1988 1997年02月 [査読有り][通常論文]
   

  We have investigated low-temperature electronic states of the organic conductors, alpha-(BEDT-TTF)(2)MHg(SCN)(4) [M=K, Rb and NH4] in terms of C-13-NMR and de susceptibility measurements. For all the compounds, the overall temperature dependence of II(T1T) scales to that of chi(x)(2) except below the nesting instability. For M=Rb and K salts, the 1/(T1T) decreased below the transition temperatures without line-broadening or relaxation enhancement. The spectra changed from complicated lines to an apparently simple Fake doublet below the nesting temperatures. All of the NMR data are successfully explained by reduction of the electronic density-of states below the transition but do not have any sign of magnetic order.
• Deuterated κ-(BEDT-TTCu[N(C]Br: A system on the borderof the superconductor-magnetic-insulator transition

  A. Kawamoto, K. Miyagawa, K. Kanoda

  Physical Review B - Condensed Matter and Materials Physics 55 21 14140 - 14143 1997年 [査読有り][通常論文]
   

  The electronic state of the deuterated salt of the organic system κ-(BEDT-TTF(Formula presented)Cu[N(CN(Formula presented)]Br, has been investigated by dc/ac susceptibility and (Formula presented)C NMR measurements. We found that the system is situated in the critical region of the transition between a superconducting phase with a (Formula presented) of ∼11.5 K and an antiferromagnetic phase with a (Formula presented) of 14-15 K. It was also found that the rapid cooling through 80 K drives the superconducting phase into the magnetic phase, that is discussed in the light of the role of disorder near the Mott transition. © 1997 The American Physical Society.
• NMR study of nesting instability

  K. Miyagawa, A. Kawamoto, K. Kanoda

  Physical Review B - Condensed Matter and Materials Physics 56 14 R8487 - R8490 1997年 [査読有り][通常論文]
   

  The low-temperature nesting instability in the quasi-two-dimensional organic conductor, (Formula presented) has been investigated by (Formula presented) NMR. Below 12 K, drastic decreases in the Knight shift and (Formula presented) were observed with neither splitting nor broadening in the NMR spectra. The (Formula presented) shows no enhancement around the nesting instability, unlike the conventional spin-density-wave (SDW) transition. The present (Formula presented) NMR data are suggestive of nonmagnetic transition but allow only an unusual case of mobile state in the SDW scenario. © 1997 The American Physical Society.
• NMR relaxation rate in the superconducting state of the organic conductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

  K Kanoda, K Miyagawa, A Kawamoto, Y Nakazawa

  PHYSICAL REVIEW B 54 1 76 - 79 1996年07月 [査読有り][通常論文]
   

  The C-13 nuclear spin-lattice relaxation rate, T-13(1)-1 has been measured in the superconducting state of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br in a field parallel to the conducting layers. The T-13(1)-1 exhibits an abrupt decrease just below the transition temperature without any indication of the Hebel-Slichter coherence peak. By separation of the vortex-dynamics contribution to T-13(1)-1 with the use of H-1-NMR, the quasiparticle contribution to T-13(1)-1 is found to follow a T-3 law that is consistent with unconventional superconductivity with line nodes in gap parameter on the Fermi surface or highly anisotropic superconductivity.
• Electron correlation in the K-phase family of BEDT-TTF compounds studied by C-13 NMR, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene

  A Kawamoto, K Miyagawa, Y Nakazawa, K Kanoda

  PHYSICAL REVIEW B 52 21 15522 - 15533 1995年12月 [査読有り][通常論文]
   

  A C-13 NMR study on kappa=(BEDT-TTF)(2)X (X = Cu(NCS)(2), Cu[N(CN)(2)]Br, and Cu[N(CN)(2)]Cl) is reported, where BEDT-TTF is bis(ethylenedithio) tetrathiafulvalene. The superconducting salts of X = Cu(NCS)2 and Cu[N(CN)(2)]Br show anamalous enhancement in nuclear spin-lattice relaxation rate T-1(-1) around 50 K, in spite of monotonic temperature dependence of the anisotropic Knight shift. On the other hand, the insulating salt of X = Cu[N(CN)(2)]Cl exhibits a divergent peak in (T1T)(-1) at 26-27 K, which is confirmed as a manifestation of an antiferromagnetic transition by broadening of the NMR line. Above 27 K, T-1(-1) shows a temperature dependence typical of critical magnetic fluctuations. The (T,T)(-1) and the line shape showed nearly the same profile for these three salts above 60 K, that gives experimental evidence for a correspondence between the anomalous enhancement of(T1T)(-1) in the superconducting salts and antiferromagnetic fluctuations established in the insulating salt of K type. The present results demonstrate the presence of strong electron correlation in both superconducting and insulating salts. Analytical expressions of T, and the Knight shift of the C-13 NMR for kappa-(BEDT-TTF)(2)X are given, which are general formulas applicable to other p pi electronic systems.
• C-13 NMR-STUDY OF LAYERED ORGANIC SUPERCONDUCTORS BASED ON BEDT-TTF MOLECULES - REPLY

  KAWAMOTO A, MIYAGAWA K, NAKAZAWA Y, KANODA K

  PHYSICAL REVIEW LETTERS 75 19 3587  1995年11月06日 [査読有り][通常論文]
  
• CHARACTERIZATION OF LOW-TEMPERATURE ELECTRONIC STATES OF THE ORGANIC CONDUCTORS ALPHA-(BEDT-TTF)(2)MHG(SCN)(4) (M=K, RB, AND NH4) BY SPECIFIC-HEAT MEASUREMENTS

  Y NAKAZAWA, A KAWAMOTO, K KANODA

  PHYSICAL REVIEW B 52 17 12890 - 12894 1995年11月 [査読有り][通常論文]
   

  The low-temperature specific heat of the organic conductors alpha-(BEDT-TTF)(2)MHg(SCN)(4) (M = K, Rb, and NH4) has been measured at temperatures down to 0.25 K and under magnetic field up to 8 T The electronic specific-heat coefficient gamma is estimated at 7.0 +/- 0.6 mJ/mol K-2 for both M = K and Rb salts and 25-26 mJ/mol K-2 for M = NH4 salt. The smaller gamma values for M = K and Rb than that for M = NH4 imply that the electron density of states of the low-temperature phase of the former two salts is suppressed down to about 35% of that of the high-temperature phase. This profile of specific heat remains unchanged up to 8 T The superconducting NH4 salt shows a very broad specific-heat peak around the transition temperature, reflecting a strong two-dimensional nature of the superconductivity.
• ANTIFERROMAGNETIC ORDERING AND SPIN STRUCTURE IN THE ORGANIC CONDUCTOR, KAPPA-(BEDT-TTF)(2)CU[N(CN)(2)]CL

  K MIYAGAWA, A KAWAMOTO, Y NAKAZAWA, K KANODA

  PHYSICAL REVIEW LETTERS 75 6 1174 - 1177 1995年08月 [査読有り][通常論文]
   

  The magnetism of an insulator, kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl, situated near the 10 K superconducting phase in kappa-type BEDT-TTF family, has been studied by H-1 NMR for the first time. A commensurate antiferromagnetic ordering with a moment of (0.4-1.0)mu(B)/dimer was found below 26-27 K. The features, quite different from the conventional spin density wave, suggest that the magnetic order is driven by strong electron correlation rather than by nesting of the Fermi surface, and that the present salt is a Mott insulator. Magnetization measurements show spin canting parallel to the conducting layer below 23 K at low fields.
• C-13 NMR-STUDY OF LAYERED ORGANIC SUPERCONDUCTORS BASED ON BEDT-TTF MOLECULES

  A KAWAMOTO, K MIYAGAWA, Y NAKAZAWA, K KANODA

  PHYSICAL REVIEW LETTERS 74 17 3455 - 3458 1995年04月 [査読有り][通常論文]
  
• C-13-NMR STUDY ON KAPPA-(BEDT-TTF)(2)X

  K MIYAGAWA, A KAWAMOTO, Y NAKAZAWA, K KANODA

  SYNTHETIC METALS 70 1-3 969 - 970 1995年03月 [査読有り][通常論文]
   

  The electronic state of the kappa phase family of BEDT-TTF compounds, kappa-(BEDT-TTF)(2)X [X=Cu(NCS)(2), Cu[N(CN)(2)]Br and Cu[N(CN)(2)]Cl], has been investigated by C-13-NMR as well as H-1-NMR. The C-13 isotope was substituted selectively into the central double bonded carbon sites of BEDT-TTF. The C-13 nuclear spin-lattice relaxation rate and line spectra have been measured for the Cu(NCS)(2) and Cu[N(CN)(2)]Br salts. The Knight shift evaluated from the the width of the spectra of the powdered samples is temperature-insensitive and scaled to the uniform susceptibility. However, the relaxation rate, T-1(-1), does not obey the Korringa law but exhibits anomalous temperature dependence with a peak formation around 50 K. The absolute value of T-1(-1) is in excess of the Korringa relation. These behaviors are considered to come from strong antiferromagnetic spin fluctuation with finite wave vector, which is suppressed below 50 K. On the other hand, the H-1 NMR and magnetization measurements gave an unambiguous evidence for antiferromagnetic transition with spin canting at 25 K in kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl. The kappa phase family, situated in the vicinity of metal-insulator and magnetic transitions, is characterized by strong electron correlations.
• RESISTIVE TRANSITION IN AN EXTREMELY 2-DIMENSIONAL SUPERCONDUCTOR, ALPHA-(BEDT-TTF)(2)NH4HG(SCN)(4)

  H SATO, H TANIGUCHI, Y NAKAZAWA, A KAWAMOTO, K KATO, K KANODA

  SYNTHETIC METALS 70 1-3 915 - 916 1995年03月 [査読有り][通常論文]
   

  In order to investigate the superconductivity in alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4), resistivity was measured as a function of temperature, magnetic field and exciting current. In addition, simultaneous measurements of I-V characteristics and ac susceptibility were carried out. The results indicate highly two-dimensional character of the superconductivity.
• SYSTEMATIC STUDY OF DCNQI-CU SALTS BY NMR AT SELECTIVE NUCLEAR SITES

  A KAWAMOTO, K MIYAGAWA, Y NAKAZAWA, K KANODA

  SYNTHETIC METALS 70 1-3 1079 - 1080 1995年03月 [査読有り][通常論文]
   

  In order to investigate electronic structure of the DCNQI-Cu systems at molecular site, we prepared C-13 labeled DMe-DCNQI and measured C-13 NMR line shapes and spin lattice relaxation rate. Comparison with the results on some partially and non-duterized DCNQI salts, lead us to get some important informations on the nature of the metallic phases.
• C-13-NMR STUDY ON ALPHA-(BEDT-TTF)(2)MHG(SCN)(4)

  K KANODA, A KAWAMOTO, K MIYAGAWA, Y NAKAZAWA

  SYNTHETIC METALS 70 1-3 973 - 974 1995年03月 [査読有り][通常論文]
   

  The low temperature electronic states of the organic conductors, alpha-(BEDT-TTF)(2)MHg(SCN)(4) [M=K, Rb], have been studied by C-13-NMR with the use of C-13 labeled samples. We observed anomalies in the nuclear spin-lattice relaxatin rate, T-1, and shift of the NMR line below 8 K for the K salt and below 12 K for the Rb salt. These indicate some phase transition. However, absence of critical fluctuation near the transition temperature and absense of splitting or broadening of the NMR line is against the static magnetic ordering as found in usual SDW systems such as the TMTSF compounds. The present results imply that the electronic density of states decreases to a half below the transition.
• Kawamoto et al. reply:

  A. Kawamoto, K. Miyagawa, Y. Nakazawa, K. Kanoda

  Physical Review Letters 75 19 3587  1995年 [査読有り][通常論文]
   

  A Reply to the Comment by H. Mayaffre, P. Wzietek and D. Jerome. © 1995 The American Physical Society.
• Electron correlation in the κ-phase family of BEDT-TTF compounds studied by C13 NMR, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene

  A. Kawamoto, K. Miyagawa, Y. Nakazawa, K. Kanoda

  Physical Review B 52 21 15522 - 15533 1995年 [査読有り][通常論文]
   

  A C13 NMR study on κ=(BEDT-TTF)2X (X=Cu(NCS)2, Cu[N(CN)2]Br, and Cu[N(CN)2]Cl) is reported, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene. The superconducting salts of X=Cu(NCS)2 and Cu[N(CN)2]Br show anamalous enhancement in nuclear spin-lattice relaxation rate T1-1 around 50 K, in spite of monotonic temperature dependence of the anisotropic Knight shift. On the other hand, the insulating salt of X=Cu[N(CN)2]Cl exhibits a divergent peak in (T1T)-1 at 26-27 K, which is confirmed as a manifestation of an antiferromagnetic transition by broadening of the NMR line. Above 27 K, T1-1 shows a temperature dependence typical of critical magnetic fluctuations. The (T1T)-1 and the line shape showed nearly the same profile for these three salts above 60 K, that gives experimental evidence for a correspondence between the anomalous enhancement of (T1T)-1 in the superconducting salts and antiferromagnetic fluctuations established in the insulating salt of κ type. The present results demonstrate the presence of strong electron correlation in both superconducting and insulating salts. Analytical expressions of T1 and the Knight shift of the C13 NMR for κ-(BEDT-TTF)2X are given, which are general formulas applicable to other pπ electronic systems. © 1995 The American Physical Society.
• Resistive Transition in an Extremely Two-Dimensional Superconductor, -(BEDT-TTF)2NH4Hg(SCN)4

  H. Sato, H. Taniguchi, Y. Nakazawa, A. Kawamoto, K. Kato, K. Kanoda

  Synthetic Metals 70 1 915 - 916 1995年 [査読有り][通常論文]
   

  In order to investigate the superconductivity in α-(BEDT-TTF)2NH4Hg(SCN)4, resistivity was measured as a function of temperature, magnetic field and exciting current. In addition, simultaneous measurements of I-V characteristics and ac susceptibility were carried out. The results indicate highly two-dimensional character of the superconductivity.
• Electronic state of κ-(BMDT-TTF)2Au(CN)2 studied by NMR and thermoelectric measurements

  Kazuya Miyagawa, Hirohiko Sato, Atsushi Kawamoto, Kazushi Kanoda, Takehiko Mori

  Synthetic Metals 70 1 879 - 880 1995年 [査読有り][通常論文]
   

  The electronic state of κ-(BMDT-TTF)2Au(CN)2 was investigated by measurements of 1H-NMR and thermoelectric power. In 1H-NMR, the profile of the nuclear relaxation curve changed drastically at 75 K from exponential time-dependence to non-single exponential one reflecting inhomogeneous. This change evidences a transition in the electronic state at this temperature. However, the longest T1 below the transition temperature behaves like a Korringa law, suggesting that the low-temperature state is another metallic state. The thermoelectric power shows a strong anomaly around 75 K, being consistent with the NMR results. Above that, the temperature dependence is similar to that found in the κ phase of BEDT-TTF compounds, suggesting a similar Fermi-surface topology. These results suggest that the transition at 75 K is not a conventional metal-to-insulator but a metal-to-metal transition.
• Specific heat study of α-(BEDT-TTF)2MHg(SCN)4

  Y. Nakazawa, H. Sato, A. Kawamoto, K. Kanoda

  Synthetic Metals 70 1 943 - 944 1995年 [査読有り][通常論文]
   

  The low-temperature specific heat of α-phase of (BEDT-TTF)2MHg(SCN)4 (M=K, Rb, NH4), where BEDT-TTF is bis-(ethylenedithio) tetrathiafulvalene, is studied. The electronic specific heat coefficient (γ) estimated from the data between 1K and 2.3K amounts to 5.3, 10.3, 28.8mJ/mol K2 for M=K, Rb and NH4, respectively. The K-salt does not have distinct anomaly around 8K within the precision of our experiments, implying that the transition occurs with a gradual change of electronic structure.
• Complex susceptibility and penetration depth of BEDT-TTF based layered superconductors

  Y. Nakazawa, H. Sato, A. Kawamoto, K. Kato, K. Kanoda

  Synthetic Metals 70 1 919 - 920 1995年 [査読有り][通常論文]
   

  We have obtained the parallel penetration depth of two representative compounds of layered organic superconductors, κ-(BEDT-TTF)2Cu[N(CN)2]Br and α-(BEDT-TTF)2NH4(SCN)4 by ac susceptibility measurements. The former salt gives the depth of 190 μm, while for the latter is 1.4 mm. These values demonstrate that the NH4(SCN)4 salt is more highly-two-dimensional than the Cu[N(CN)2]Br salt. The ac susceptibility under dc magnetic field probes peculiarities of the vortex dynamics.
• De Haas-van Alphen effect in κ-(DMET)2AuBr2

  K. Kanoda, K. Kato, A. Kawamoto, K. Oshima, T. Takahashi, K. Kikuchi, K. Saito, I. Ikemoto

  Synthetic Metals 56 1 2309 - 2313 1993年03月29日 [査読有り][通常論文]
   

  We have performed magnetization measurements of the title compound up to 12 tesla and down to 0.5 K in order to examine the Fermi-surface topology. The de Haas-van Alphen effect has been clearly observed. This is the first report on the quantum oscillation in κ-phase compound other than the BEDT-TTF salts. The oscillation has two components with different frequencies. The faster one corresponds just to the cross-sectional area of the 1st Brillouin zone and the other to 21 % of that. Such a cross-sectional profile of the Fermi surface is essentially the same as in the κ-phase of BEDT-TTF compounds. However, the simultaneous oscillation even at low field in this system is different from the result for κ-(BEDT-TTF)2Cu(NCS)2, where the faster oscillation is reported to occur only at higher field as a magnetic breakdown effect. The present result implies that κ-(DMET)2AuBr2 has no gap against the crossing of the Fermi surface at the zone boundary unlikely κ-(BEDT-TTF)2Cu(NCS)2. This comes from the difference in the space group of the two crystals. The effective mass for each orbit is estimated. © 1993.
• Der dreidimensionale Aufbau von unsymmetrischen Protonen-Elektronen-Transfersystemen mit Disulfidbrücke - der Bis(4-hydroxyphenyl)disulfid-Benzochinon-Komplex

  Kenichi Sugiura, Jiro Toyoda, Hiroshi Okamoto, Kaoru Okaniwa, Tadaoki Mitani, Atsushi Kawamoto, Jiro Tanaka, Kazuhiro Nakasuji

  Angewandte Chemie 104 7 877 - 879 1992年07月
• Crystal Structures of Metallic and Insulating Molecular Complexes between Naphthaceno(5,6-cd: 11,12-c'd')bis(1,2)diselenole and 4,8-Bis(dicyanomethylene)-4H,8H-benzo(1,2-c: 4,5-c')bis(1,2,5)thiadiazole: (TSeN)(BTDA-TCNQ)and(TSeN)(BTDA-TCNQ)(C6H5Cl).

  Iwasaki Kentaro, Ugawa Akito, Kawamoto Atsushi, Yamashita Yoshiro, Yakushi Kyuya, Suzuki Takanori, Miyashi Tsutomu

  Bulletin of the Chemical Society of Japan 65 12 3350 - 3357 The Chemical Society of Japan 1992年 

  The charge-transfer complex between naphthaceno[5,6-cd:11,12-c′d′]bis[1,2]diselenole (TSeN) and 4,8-bis(dicyanomethylene)-4H,8H-benzo[1,2-c:4,5-c′]bis[1,2,5]thiadiazole (BTDA-TCNQ) is found to show at least three different types of crystal modifications; insulating Type-I has a (1 : 1 : 1) ratio containing solvent molecules (chlorobenzene), metallic Type-II has a (1 : 1) stoichiometry, and semiconductive Type-III is conjectured to have a (1 : 2) or (2 : 1) stoichiometry. The crystal structures of Type-I and Type-II were determined by a single-crystal X-ray diffraction method. Type-I comprises mixed-stack molecular columns, and Type-II segregated-stack molecular columns. In both types the neighboring columns are linked along short molecular axes by two Se···N contacts that are shorter than the corresponding van der Waals contact. In the Type-II crystal, there are other short distances between TSeN and BTDA-TCNQ in the direction of the long molecular axes. From the C=C bond length in the C=C(CN)₂ group of BTDA-TCNQ, the degrees of charge transfer of these molecular complexes were estimated as 0.2 ± 0.3 in Type-I and 0.9 ± 0.2 in Type-II.
• Three‐Dimensional Structure of an Unsymmetrical Proton–Electron Transfer System Containing a Disulfide Bond: The Bis(4‐hydroxy‐phenyl)disulfide‐Benzoquinone Complex

  Kenichi Sugiura, Jiro Toyoda, Hiroshi Okamoto, Kaoru Okaniwa, Tadaoki Mitani, Atsushi Kawamoto, Jiro Tanaka, Kazuhiro Nakasuji

  Angewandte Chemie International Edition in English 31 7 852 - 854 1992年 [査読有り][通常論文]
   

  Three factors determine the three‐dimensional crystal structure of the charge‐transfer complex of bis(4‐hydroxyphenyl)disulfide and 1,4‐benzoquinone: the charge‐transfer interaction between the components, the hydrogen bonds, and the twist of the phenyl rings about the SS bond of the disulfide unit. The ribbon‐shaped structures depicted on the right result, which line up along the c axis. (Figure Presented.) Copyright © 1992 by VCH Verlagsgesellschaft mbH, Germany
• THE CRYSTAL-STRUCTURE AND PHYSICAL-PROPERTIES OF THE 3-2 CHARGE-TRANSFER COMPLEX OF BIS(ETHYLENEDITHIO)DITHIAPYRENE (ETDTPY) AND DIBENZOBARRELENOTETRACYANOQUINODIMETHANE (DBBTCNQ)

  J TOYODA, K NAKASUJI, T KOTANI, MURATA, I, A KAWAMOTO, J TANAKA

  CHEMISTRY LETTERS 7 1237 - 1240 1991年07月 [査読有り][通常論文]
   

  The V-shape correlation between h-upsilon-CT and DELTA-E(o,r) of the charge transfer complexes is convenient to judge the gross features of the solid state properties. Using this correlation, we found the 3:2 charge transfer complex of bis(ethylenedithio)dithiapyrene (ETDTPY) and dibenzobarrelenotetracyanoquinodimethane (DBBTCNQ) which showed the columnar structure of alternating trimeric stack of the donor and dimeric stack of the acceptor.
• NEW MOLECULAR-METALS COMPOSED OF PERICONDENSED HETEROCYCLES

  K NAKASUJI, J TOYODA, K IMAEDA, H INOKUCHI, MURATA, I, A ODA, A KAWAMOTO, J TANAKA

  SYNTHETIC METALS 42 3 2529 - 2534 1991年05月 [査読有り][通常論文]
   

  We reported design and synthesis of new peri-condensed heterocycles which do not contain TTF type conjugated systems, that is, three isomers of dithiaperylenes (DTPR), one isomer of dithiapyrene (DTPY) and their methylthio or methylseleno derivatives. These donors showed two-stage redox behavior whose potentials are comparable to that of TTF. Good correlation was obtained between the oxidation potentials and the HOMO energies calculated by the PM3 method. A number of CT complexes prepared were classified into three groups, neutral, ionic, and non-V-shape groups. Among them, the non-V-shape group complexes contained highly conducting complexes including molecular metals. Most of the CT salts with inorganic anions having high conductivities showed lower electronic transition energies than 0.5 eV.
• Metallic behavior stable against Peierls instability in the one-dimensional organic conductor tetraselenotetracene-bis(1,2,5-thiadiazolo)tetracyanoquinodimethane [(TSeT)-(BTDA-TCNQ)]

  A. Ugawa, K. Iwasaki, A. Kawamoto, K. Yakushi, Y. Yamashita, T. Suzuki

  Physical Review B 43 18 14718 - 14721 1991年 [査読有り][通常論文]
   

  Tetraselenotetracene (TSeT) forms a charge-transfer complex with bis(1,2,5-thiadiazolo)tetracyanoquinodimethane (BTDA-TCNQ), the complex showing a metallic behavior down to 1.5 K without undergoing a Peierls transition. The structure consists of segregated columns of TSeT and BTDA-TCNQ molecules, among which there also exist short intermolecular contacts. The polarized reflectance spectra indicate that the material is a one-dimensional metal in contrast to the structural features. The electronic structure is characterized by a one-dimensional conduction band lying on the two-dimensional lattice, which prevents the system from undergoing a Peierls distortion. © 1991 The American Physical Society.
• ELECTRONIC-STRUCTURES OF 2,7-BIS(METHYLTHIO)-1,6-DITHIAPYRENE (MTDTPY) CHARGE-TRANSFER COMPLEXES

  A KAWAMOTO, J TANAKA, M SASAKI, MURATA, I, K NAKASUJI

  BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 63 8 2146 - 2149 1990年08月 [査読有り][通常論文]
  
• CRYSTAL AND ELECTRONIC-STRUCTURES OF RADICAL SALTS OF 2,7-BIS(METHYLTHIO)-1,6-DITHIAPYRENE (MTDTPY) AND 2,7-BIS(METHYLSELENO)-1,6-DITHIAPYRENE (MSDTPY)

  A KAWAMOTO, J TANAKA, A ODA, H MIZUMURA, MURATA, I, K NAKASUJI

  BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 63 8 2137 - 2145 1990年08月 [査読有り][通常論文]
  
• PREPARATION, CRYSTAL-STRUCTURE, AND SOLID-STATE PROPERTIES OF HIGHLY CONDUCTIVE (PHTHALOCYANINATO)PLATINUM RADICAL SALTS - PTPC(CLO4)0.5 AND PTPC(ASF6)X

  H YAMAKADO, K YAKUSHI, N KOSUGI, H KURODA, A KAWAMOTO, J TANAKA, T SUGANO, M KINOSHITA, S HINO

  BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 62 7 2267 - 2272 1989年07月 [査読有り][通常論文]
  
• ELECTROCHEMICAL PREPARATION AND CHARACTERIZATION OF THE RADICAL SALTS OF (PHTHALOCYANINATO)NICKEL, NIPC(SBF6)0.5, AND NIPC(ASF6)0.5

  K YAKUSHI, H YAMAKADO, M YOSHITAKE, N KOSUGI, H KURODA, T SUGANO, M KINOSHITA, A KAWAMOTO, J TANAKA

  BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 62 3 687 - 696 1989年03月 [査読有り][通常論文]
  
• PHYSICAL-PROPERTIES OF BETA-(BEDT-TTF)2ICL2

  A UGAWA, Y OKAWA, K YAKUSHI, H KURODA, A KAWAMOTO, J TANAKA, M TANAKA, Y NOGAMI, S KAGOSHIMA, K MURATA, T ISHIGURO

  SYNTHETIC METALS 27 1-2 A407 - A412 1988年12月 [査読有り][通常論文]
  
• CRYSTAL-STRUCTURE AND POLARIZED REFLECTANCE SPECTRA OF ALPHA'-(BIS(ETHYLENEDITHIO)-TETRATHIAFULVALENIUM)2-BROMOIODOAURATE, ALPHA'-(BEDT-TTF)2IAUBR

  A UGAWA, K YAKUSHI, H KURODA, A KAWAMOTO, J TANAKA

  SYNTHETIC METALS 22 4 305 - 315 1988年02月 [査読有り][通常論文]
  
• A new ambient pressure organic superconductor based on BEDT-TTF with Tc higher than 10K (Tc=10.4K).

  Urayama Hatsumi, Yamochi Hideki, Saito Gunzi, Nozawa Kiyokazu, Sugano Tadashi, Kinoshita Minoru, Sato Shoichi, Oshima Kokichi, Kawamoto Atsushi, Tanaka Jiro

  Chemistry Letters 1 55 - 58 The Chemical Society of Japan 1988年 

  An ambient pressure superconductivity of (BEDT-TTF)₂Cu(SCN)₂ was observed by d.c. magnetic susceptibility and electrical conductivity measurements. The superconducting critical temperature is the highest (T_C=10.4 K) among the organic superconductors so far obtained, even though the anion has a positional disorder in the crystal.
• Preparation and characterization of (tetrabenzoporphyrinato)nickel hexafluoroarsenate, (NiTBP)3(AsF6)2(C10H7Cl). A new type of metallomacrocyclic radical salts.

  Yakushi Kyuya, Yoshitake Michiko, Kuroda Haruo, Kawamoto Atsushi, Tanaka Jiro, Sugano Tadashi, Kinoshita Minoru

  Bulletin of the Chemical Society of Japan 61 5 1571 - 1576 The Chemical Society of Japan 1988年 

  Single crystals of a (tetrabenzoporphyrinato)nickel hexafluoroarsenate, (NiTBP)₃(AsF₆)₂ were prepared by the use of an electrochemical technique. NiTBP is stacked one-dimensionally with a periodic unit composed of three macrocycles. This stacking mode is a new type among the one-dimensionally stacked macrocyclic complexes. The experimental results on reflectance spectrum and ESR indicate that this material is a one-dimensional semiconductor with a small electron correlation.
• Synthesis of optically active 2,2′‐diselenocyanato‐1,1′‐binaphthyl and its molecular structure. Hypervalent nature of divalent selenium atom in crystal state

  Shuji Tomoda, Michio Iwaoka, Kyuya Yakushi, Atsushi Kawamoto, Jiro Tanaka

  Journal of Physical Organic Chemistry 1 3 179 - 184 1988年 [査読有り][通常論文]
   

  2,2′‐Diselenocyanato‐1,1′‐binaphthyl(1), the first selenium‐containing binaphthyl derivative, has been synthesized in optically active form the corresponding diamine by diazotization followed by the reaction with potassium selenocyanate. Its molecular structure is determined by X‐ray diffraction method. It is revealed that selenium atoms have hypervalent penta‐coordination in the crystal. Copyright © 1988 John Wiley & Sons Ltd.
• METHYLTHIO-SUBSTITUTED AND ETHANEDIYLDITHIO-SUBSTITUTED 1,6-DITHIAPYRENES AND THEIR CHARGE-TRANSFER COMPLEXES - NEW ORGANIC MOLECULAR-METALS

  K NAKASUJI, M SASAKI, T KOTANI, MURATA, I, T ENOKI, K IMAEDA, H INOKUCHI, A KAWAMOTO, J TANAKA

  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 109 23 6970 - 6975 1987年11月 [査読有り][通常論文]
  
• CHARGE-TRANSFER COMPLEXES OF PERICONDENSED WEITZ-TYPE DONORS - 3,10-DITHIAPERYLENE, 1,6-DITHIAPYRENE, AND THEIR DERIVATIVES

  K NAKASUJI, T KOTANI, MURATA, I, A KAWAMOTO, J TANAKA, T ENOKI, K IMAEDA, H INOKUCHI

  SYNTHETIC METALS 19 1-3 385 - 388 1987年03月 [査読有り][通常論文]
  
• Crystal structure and electrical properties of (BEDT-TTF)3Br2(H2O)2.

  Urayama Hatsumi, Saito Gunzi, Kawamoto Atsushi, Tanaka Jiro

  Chemistry Letters 9 1753 - 1756 The Chemical Society of Japan 1987年 

  A small anion, Br⁻, forms a metallic 3:2 BEDT-TTF salt with an inclusion of water. In the crystal two water molecules and two bromide anions form a cluster which behaves as a dianion group. The measurement of the electric resistivity indicates that this material has a metal-insulator transition at 185 K.
• MAGNETIC AND OPTICAL-PROPERTIES OF (BEDT-TTF)CUCL2 COMPLEX

  M TANAKA, A KAWAMOTO, J TANAKA, M SANO, T ENOKI, H INOKUCHI

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 26 893 - 894 1987年 [査読有り][通常論文]
  
• Crystal structure and reflectance spectrum of .BETA."-(BEDT-TTF)2IAuBr.

  Ugawa Akito, Yakushi Kyuya, Kuroda Haruo, Kawamoto Atsushi, Tanaka Jiro

  Chemistry Letters 11 1875 - 1878 The Chemical Society of Japan 1986年 

  (BEDT-TTF)₂IAuBr was synthesized and the crystal structure of this material was determined to be of the β″- type, being isomorphous to β″-(BEDT-TTF)₂AuBr₂. The polarized reflectance spectrum indicates that the electronic structure of this salt is of considerable two-dimensional character.
• Synthesis and crystal structure of a highly conducting (phthalocyaninato)nickel hexafluoroantimonate, (NiPc)2SbF6.

  Yakushi Kyuya, Sakuda Makoto, Kuroda Haruo, Kawamoto Atsushi, Tanaka Jiro

  Chemistry Letters 7 1161 - 1164 The Chemical Society of Japan 1986年 

  Sigle crystals of a metallic (phthalocyaninato)nickel hexafluoro antimonate, (NiPc)₂SbF₆, were newly prepared by the use of an electrochemical technique. NiPc is stacked one-dimensionally in a slight zigzag way, which quite resembles the structure of highly conducting NiPcI.
• Crystal structure of .ALPHA.-(BEDT-TTF)3(ReO4)2.

  Kanbara Hirohisa, Tajima Hiroyuki, Aratani Sukekazu, Yakushi Kyuya, Kuroda Haruo, Saito Gunzi, Kawamoto Atsushi, Tanaka Jiro

  Chemistry Letters 3 437 - 440 The Chemical Society of Japan 1986年 

  The two-dimensional strucrture of α-(BEDT-TTF)₃(ReO₄)₂ on the (010) plane is very similar to that of (BEDT-TTF)₃(ClO₄)₂, although the three dimensional structure is quite different from each other. The slight geometrical difference between the crystallographically independent molecules suggests the different formal charge of these molecules.

その他活動・業績

• ^69,71Ga-NMR測定によるλ-(BEDSe-TTF)₂GaCl₄の特異な圧力誘起電子相の観測

  安村乃絵瑠, 小林拓矢, 谷口弘三, 福岡脩平, 河本充司 日本物理学会講演概要集(CD-ROM) 77 (1) 2022年
• Thermodynamic evidence for the formation of a Fulde-Ferrell-Larkin-Ovchinnikov phase in the organic superconductor $λ$-(BETS)$_2$GaCl$_4$

  Shusaku Imajo, Takuya Kobayashi, Atsushi Kawamoto, Koichi Kindo, Yasuhiro Nakazawa 2021年05月27日 

  In this work, the thermodynamic properties of the organic superconductor $\lambda$-(BETS)$_2$GaCl$_4$ are investigated to study a high-field superconducting state known as the putative Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. We observed a small thermodynamic anomaly in the field $H_{\rm FFLO}$ $\sim$ 10~T, which corresponds to the Pauli limiting field $H_{\rm P}$. This anomaly probably originates from a transition from a uniform superconducting state to the FFLO state. $H_{\rm FFLO}$ does not show a strong field-angular dependence due to a quasi-isotropic paramagnetic effect in $\lambda$-(BETS)$_2$GaCl$_4$. The thermodynamic anomaly at $H_{\rm FFLO}$ is smeared out and low-temperature upper critical field $H_{\rm c2}$ changes significantly if fields are not parallel to the conducting plane even for a deviation of $\sim$0.5$^{\circ}$. This behavior indicates that the high-field state is very unstable, as it is influenced by the strongly anisotropic orbital effect. Our results are consistent with the theoretical predictions on the FFLO state, and show that the high-field superconductivity is probably an FFLO state in $\lambda$-(BETS)$_2$GaCl$_4$ from a thermodynamic point of view.
• 有機超伝導体λ-(BETS)₂GaCl₄の超伝導相近傍の相図

  小林拓矢, 河本充司 日本物理学会誌 76 (7) 2021年
• λ-(BEST)₂GaCl₄塩の^69,71Ga-NMR

  河本充司, 福岡脩平, 小川巧真, 伊藤悠馬, 伊藤有咲, 小林拓矢, 谷口弘三 日本物理学会講演概要集(CD-ROM) 76 (1) 2021年
• λ-(BETS)₂GaBr_xCl_4-x(x=0.9)の¹³C-NMR

  岡太耀, 河本充司, 澤田賢志, 石川貴子, 小林拓矢 日本物理学会講演概要集(CD-ROM) 76 (1) 2021年
• 微視的測定手法による有機電荷移動錯体λ-(BEST)₂GaCl₄の反強磁性秩序の観測

  小林拓矢, 伊藤有咲, SARI Dita Puspita, SARI Dita Puspita, 渡邊功雄, 斉藤洋平, 河本充司, 佐藤一彦, 谷口弘三 日本物理学会講演概要集(CD-ROM) 76 (1) 2021年
• ⁶³Cu-NQRによるκ型ET塩のゼロ磁場磁気構造の微視的検証

  山崎大誠, 小林拓矢, 加藤優樹, 綱川仁志, 佐藤一彦, 谷口弘三, 河本充司 日本物理学会講演概要集(CD-ROM) 76 (2) 2021年
• 有機超伝導体κ-(BEDT-TTF)₂Cu[N(CN)₂]Brのゼロ磁場下⁶³Cu-NQRによる研究

  小澤宏彬, 小林拓矢, 綱川仁志, 生沼浩介, 佐藤一彦, 谷口弘三, 河本充司 日本物理学会講演概要集(CD-ROM) 75 (1) 2020年
• λ-(BETS)₂GaBr_0.75Cl_3.25の¹³C-NMR

  石川貴子, 澤田賢志, 大沼晃浩, 河本充司, 小林拓矢 日本物理学会講演概要集(CD-ROM) 75 (1) 2020年
• π-d系物質λ-(BEDT-STF)₂FeCl₄の誘電特性

  福岡脩平, 伊藤悠馬, 高橋仁徳, 松永悟明, 井原慶彦, 河本充司 日本物理学会講演概要集(CD-ROM) 75 (2) 2020年
• λ‐(BEDT‐STF)₂FeCl₄の磁気秩序状態に関する熱的研究

  福岡脩平, 南舘孝亮, 松永悟明, 野村一成, 井原慶彦, 河本充司 日本物理学会講演概要集(CD-ROM) 74 (1) ROMBUNNO.17aB211‐7 2019年03月22日 [査読無し][通常論文]
  
• 有機超伝導体λ-(BETS)₂GaCl₄の^69/71Ga-NMR法を用いた電荷/スピン異常の選択的検出

  辻晃平, 小林拓矢, 河本充司 日本物理学会講演概要集(CD-ROM) 74 (1) 2019年
• ⁶³Cu-NQRによるκ-(BEDT-TTF)₂Cu₂(CN)₃の研究

  小林拓矢, 小林拓矢, 古川裕次, DING Qing-Ping, 河本充司, 佐藤一彦, 谷口弘三 日本物理学会講演概要集(CD-ROM) 74 (2) 2019年
• ⁶³Cu-NQRによるκ-(ET)₂Cu[N(CN)₂]Clの磁気構造の研究

  綱川仁志, 生沼浩介, 小林拓矢, 谷口弘三, 佐藤一彦, 河本充司 日本物理学会講演概要集(CD-ROM) 74 (2) 2019年
• 有機分子を挿入したTTF-CA類縁体の電子状態

  三枝大輔, 福岡脩平, 井原慶彦, 河本充司, 高橋幸裕, 竹久美佳, 田中恵里, 原田潤, 稲辺保 日本物理学会講演概要集(CD-ROM) 74 (2) 2019年
• β“‐(BEDT‐TTF)₄[(H₃O)Ga(C₂O₄)₃]・C₆H₅NO₂のSTM/STS

  市村晃一, 小久保宏樹, 丹田聡, 黒澤徹, 小田研, 本間弘樹, 松永悟明, 森部一斗, 井原慶彦, 河本充司 日本物理学会講演概要集(CD-ROM) 73 (2) ROMBUNNO.11aK302‐7 2018年09月21日 [査読無し][通常論文]
  
• ¹³C NMR測定によるπ‐d系物質λ‐(BEDT‐STF)₂FeCl₄の低温磁気状態の研究

  福岡脩平, 南舘孝亮, 松永悟明, 野村一成, 井原慶彦, 河本充司 日本物理学会講演概要集(CD-ROM) 73 (2) ROMBUNNO.12aK302‐7 2018年09月21日 [査読無し][通常論文]
  
• 擬一次元有機導体(TMTTF)₂XのSTM分光

  本間弘樹, 延兼啓純, 市村晃一, 河本充司, 松永悟明 日本物理学会講演概要集(CD-ROM) 73 (1) ROMBUNNO.25pB404‐6 -1847 2018年03月23日 [査読無し][通常論文]
  
• 有機超伝導体における強磁場中異常超伝導状態の微視的研究

  井原慶彦, 福岡脩平, 河本充司, GOMES‐GARCIA Carlos J, 佐々木孝彦 東北大学金属材料研究所強磁場超伝導材料研究センター年次報告 2016 55 2017年06月 [査読無し][通常論文]
  
• S=1/2カゴメ格子反強磁性体CaCu₃(OH)₆Cl₂・0.6H₂Oの³⁵Cl‐NMRによる研究

  吉田紘行, 井原慶彦, 野口直彌, 石井裕人, 高田篤, 木田孝則, 鳴海康雄, 萩原政幸, 河本充司, 佐々木孝彦, 小田研 日本物理学会講演概要集(CD-ROM) 72 (1) ROMBUNNO.19pC31‐9 -1247 2017年03月21日 [査読無し][通常論文]
   

  CaCu_3_(OH)_6_Cl_2_・0.6H_2_OはS = 1/2カゴメ格子反強磁性体の良いモデル物質である。本講演では、19 Tまでの粉末強磁場NMR、5.5 Tまでの単結晶NMRの結果を報告し、CaCu_3_(OH)_6_Cl_2_・0.6H_2_Oの基底状態について議論する。

• κ-(ET)₂Cu[N(CN)₂]Iにおける圧力下¹³C-NMR測定

  鈴田耀大, 小林拓矢, 井原慶彦, 河本充司 日本物理学会講演概要集(CD-ROM) 72 (1) 2017年
• β’-(BEDT-TTF)₂ICl₂における分子運動と電子状態

  福岡脩平, 三枝大輔, 澤田賢志, 江頭由浩, 井原慶彦, 河本充司 日本物理学会講演概要集(CD-ROM) 72 (2) 2017年
• κ‐(BEDT‐TTF)₂Cu[N(CN)₂]Brにおける異方的超伝導ギャップ:STM分光

  生松倫太郎, 延兼啓純, 松永悟明, 野村一成, 河本充司 日本物理学会講演概要集(CD-ROM) 71 (1) ROMBUNNO.21ABC‐4 -1596 2016年03月22日 [査読無し][通常論文]
   

  有機超伝導体!LaTeX$\kappa$-(BEDT-TTF)_2_Xではアニオン層Xに化学置換を施すことで電子相関を制御可能である。本研究では電子相関の異なるX=Cu[N(CN)_2_]Br及びCu(NCS)_2_に対しエネルギーギャップの検出が可能な偏光時間分解分光を実施した。その結果、両試料において擬ギャップ応答と考えられる空間対称性破れを検出することに成功した。さらに超伝導応答が、電子相関がより大きいX=Cu[N(CN)_2_]Brの試料では転移温度以上においても検出され、超伝導発現における電子相関の重要性を示唆する結果が得られた。

• 21aBC-4 κ-(BEDT-TTF)_2Cu[N(CN)_2]Brにおける異方的超伝導ギャップ : STM分光

  生松 倫太郎, 延兼 啓純, 松永 悟明, 野村 一成, 河本 充司 日本物理学会講演概要集 71 (1) 1894 -1894 2016年03月19日 [査読無し][通常論文]
  
• 22pBE-5 Probing the Superconducting Ground State Organic Superconductor λ-(BETS)_2GaCl_4 by μSR

  Sari D. P., Asih R., Hiraki K., Ishii Y., Kumagai H., Kawamoto A., Takahashi T., Watanabe I., Nakano T., Nozue Y. 日本物理学会講演概要集 71 1954 -1954 2016年
• 電荷密度の空間的不均一を内在する有機超伝導体

  井原慶彦, 河本充司 固体物理 50 (1) 1 -9 2015年01月15日 [査読無し][通常論文]
  
• 8pAG-3 ^<13>C-NMRを用いたκ-(BEDT-TTF)_2Cu[N(CN)_2]Iにおける超格子構造の研究(8pAG κ型ET塩他(Mott転移など),領域7(分子性固体))

  小林 拓矢, 井原 慶彦, 河本 充司 日本物理学会講演概要集 69 (2) 606 -606 2014年08月22日
• 強磁場下¹³C NMR測定による有機超伝導体β”‐(BEDT‐TTF)₄[(H₃O)Ga(C₂O₄)₃]・C₆H₅NO₂の電荷秩序状態の研究

  井原慶彦, JEONG M, MAYAFFRE H, BERTHIER C, HORVATIC M, 関春海, 河本充司 日本物理学会講演概要集 69 (2) 589 2014年08月22日 [査読無し][通常論文]
  
• 高圧力下におけるκ‐(ET)₂Cu₂(CN)₃のラマン分光

  薬師久彌, 山本薫, 斉藤洋平, 河本充司 日本物理学会講演概要集 69 (2) 599 2014年08月22日 [査読無し][通常論文]
  
• κ‐(BEDT‐TTF)₂X(X=Cu[N(CN)₂]Br,Cu(NCS)₂)の¹³C NMRスペクトル測定による超微細結合テンソルの見積もり

  斉藤洋平, 河本充司 日本物理学会講演概要集 69 (2) 606 -606 2014年08月22日 [査読無し][通常論文]
  
• ¹³C‐NMRを用いたκ‐(BEDT‐TTF)₂Cu[N(CN)₂]Iにおける超格子構造の研究

  小林拓矢, 井原慶彦, 河本充司 日本物理学会講演概要集 69 (2) 606 2014年08月22日 [査読無し][通常論文]
  
• 30aCL-10 ^<13>C-NMRを用いたκ-(BEDT-TTF)_2Cu[N(CN)_2]BrのBEDT-STFドープによる不純物効果の研究(30aCL κ型ET塩他(スピン液体・モット転移・超伝導等),領域7(分子性固体))

  小林 拓矢, 井原 慶彦, 河本 充司 日本物理学会講演概要集 69 (1) 865 -865 2014年03月05日
• 28aBC-10 ^<13>C-NMR法によるα-(BEDT-TTF)_2MHg(SCN)_4 M=(NH_4,Rb)のサイト依存電子状態測定(28aBC 擬1次元系・電荷秩序など,領域7(分子性固体))

  野田 航生, 井原 慶彦, 河本 充司 日本物理学会講演概要集 69 (1) 842 -842 2014年03月05日
• 27pBC-9 ^<13>C-NMR測定によるβ"-(BEDT-TTF)_4[(H_3O)Fe(C_2O_4)_3]-C_6H_5Brのπ-d相互作用の研究(27pBC π-d系(BETS)・磁性・超伝導,領域7(分子性固体))

  二見 洋輔, 井原 慶彦, 河本 充司, Gomez-Garcia Carlos J. 日本物理学会講演概要集 69 (1) 833 -833 2014年03月05日
• 30aCL-9 有機超伝導体κ-(ET)_2Cu[N(CN)_2]Brの角度分解STS(30aCL κ型ET塩他(スピン液体・モット転移・超伝導等),領域7(分子性固体))

  岡 雄基, 延兼 啓純, 松永 悟明, 野村 一成, 河本 充司, 上遠野 一広, 市村 晃一 日本物理学会講演概要集 69 (1) 865 -865 2014年03月05日 [査読無し][通常論文]
  
• ¹³C‐NMR法によるα‐(BEDT‐TTF)₂MHg(SCN)₄M=(NH₄,Rb)のサイト依存電子状態測定

  野田航生, 井原慶彦, 河本充司 日本物理学会講演概要集 69 (1) 842 2014年03月05日 [査読無し][通常論文]
  
• 有機超伝導体κ‐(ET)₂Cu[N(CN)₂]Brの角度分解STS

  岡雄基, 延兼啓純, 松永悟明, 野村一成, 河本充司, 上遠野一広, 市村晃一 日本物理学会講演概要集 69 (1) 865 2014年03月05日 [査読無し][通常論文]
  
• ¹³C‐NMRを用いたκ‐(BEDT‐TTF)₂Cu[N(CN)₂]BrのBEDT‐STFドープによる不純物効果の研究

  小林拓矢, 井原慶彦, 河本充司 日本物理学会講演概要集 69 (1) 865 2014年03月05日 [査読無し][通常論文]
  
• ¹³C‐NMR測定によるβ”‐(BEDT‐TTF)₄[(H₃O)Fe(C₂O₄)₃]‐C₆H₅Brのπ‐d相互作用の研究

  二見洋輔, 井原慶彦, 河本充司, GOMEZ‐GARCIA Carlos J 日本物理学会講演概要集 69 (1) 833 2014年03月05日 [査読無し][通常論文]
  
• 27pDJ-10 (TMTTF)_2PF_6のスピン密度波相における非線形電気伝導の圧力依存性(擬一次元系,密度波,領域7(分子性個体・有機導体))

  山浦 大輔, 山本 真生, 松永 悟明, 野村 一成, 河本 充司 日本物理学会講演概要集 68 (2) 775 -775 2013年08月26日
• 27aDJ-7 ^<13>C NMR測定による有機超伝導体β"-(BEDT-TTF)_4 [(H_3O)Ga(C_2O_4)_3]・C_6H_5NO_2の100K異常の研究(β'型ET塩,強誘電,熱電等,領域7(分子性個体・有機導体))

  井原 慶彦, 二見 洋輔, 関 春海, 河本 充司 日本物理学会講演概要集 68 (2) 767 -767 2013年08月26日
• 27aDJ-8 有機超伝導体β"-(BEDT-TTF)_4[(H_3O)Ga(C_2O_4)_3]・C_6H_5NO_2のSTM分光(β'型ET塩,強誘電,熱電等,領域7(分子性個体・有機導体))

  高橋 周, 岡 雄基, 延兼 啓純, 松永 悟明, 野村 一成, 関 春海, 井原 慶彦, 河本 充司 日本物理学会講演概要集 68 (2) 767 -767 2013年08月26日
• 28aDJ-10 有機超伝導体κ-(BEDT-TTF)_2Cu(NCS)_2の面内角度分解NMRによる超伝導対称性の研究(κ型ET塩等,領域7(分子性個体・有機導体))

  斉藤 洋平, 小林 拓矢, 井原 慶彦, 河本 充司 日本物理学会講演概要集 68 (2) 781 -781 2013年08月26日
• 有機超伝導体β” (BEDT‐TTF)₄[(H₃O)Ga(C₂O₄)₃]・C₆H₅NO₂のSTM分光

  高橋周, 岡雄基, 延兼啓純, 松永悟明, 野村一成, 関春海, 井原慶彦, 河本充司 日本物理学会講演概要集 68 (2) 767 2013年08月26日 [査読無し][通常論文]
  
• 27pXN-13 片側置換による(TMTSF)_2PF_6の^<13>C-NMR (II)(27pXN 擬一次元系,パイエルス転移,領域7(分子性固体・有機導体))

  永田 真斗, 井原 慶彦, 河本 充司 日本物理学会講演概要集 68 (1) 940 -940 2013年03月26日
• 27pXN-4 (TMTTF)_2SbF_6の^<13>C-NMR(27pXN 擬一次元系,パイエルス転移,領域7(分子性固体・有機導体))

  山本 真稔, 下原 直樹, 佐藤 健人, 松永 悟明, 野村 一成, 居初 知征, 広瀬 真史, 河本 充司 日本物理学会講演概要集 68 (1) 939 -939 2013年03月26日
• 29aXN-7 κ-BEDT-TTF塩のラマン分光(29aXN ダイマーモット絶縁体,領域7(分子性固体・有機導体))

  薬師 久彌, ドロズドバ オルガ, 清水 康弘, 斎藤 軍治, 河本 充司, 山本 貴 日本物理学会講演概要集 68 (1) 959 -959 2013年03月26日
• 26aXN-3 NMRを用いた有機超伝導体における近接効果の研究(26aXN BEDT-TTF系,層状超伝導体,領域7(分子性固体・有機導体))

  斉藤 洋平, 井原 慶彦, 河本 充司 日本物理学会講演概要集 68 (1) 900 -900 2013年03月26日
• 26aXN-8 ^<13>C-NMRによるκ-(BEDT-TTF)_2Cu[N(CN)_2]Clにおける線幅異常の研究(26aXN BEDT-TTF系,層状超伝導体,領域7(分子性固体・有機導体))

  松本 実子, 河本 充司 日本物理学会講演概要集 68 (1) 901 -901 2013年03月26日
• 26aXN-7 有機超伝導体β"-(BEDT-TTF)_4[(H_3O)Ga(C_2O_4)_3]・C_6H_5NO_2における超伝導転移直上の電荷秩序(26aXN BEDT-TTF系,層状超伝導体,領域7(分子性固体・有機導体))

  井原 慶彦, 関 春海, 河本 充司 日本物理学会講演概要集 68 (1) 901 -901 2013年03月26日
• 26aXN-1 ^<13>C-NMR測定によるк-(BEDT-TTF)_2Cu[N(CN)_2]Brの反強磁性と超伝導の研究(26aXN BEDT-TTF系,層状超伝導体,領域7(分子性固体・有機導体))

  小林 拓矢, 斉藤 洋平, 井原 慶彦, 河本 充司 日本物理学会講演概要集 68 (1) 900 -900 2013年03月26日
• 26aXN-2 к-(ET)_2XのFIB加工面におけるSTM分光 : 超伝導ギャップの対称性(26aXN BEDT-TTF系,層状超伝導体,領域7(分子性固体・有機導体))

  鈴木 資生, 岡 雄基, 延兼 啓純, 松永 悟明, 野村 一成, 河本 充司 日本物理学会講演概要集 68 (1) 900 -900 2013年03月26日 [査読無し][通常論文]
  
• κ‐(ET)₂XのFIB加工面におけるSTM分光:超伝導ギャップの対称性

  鈴木資生, 岡雄基, 延兼啓純, 松永悟明, 野村一成, 河本充司 日本物理学会講演概要集 68 (1) 900 2013年03月05日 [査読無し][通常論文]
  
• ¹³C-NMR測定によるκ-(BEDT-TTF)₂Cu[N(CN)₂]Brの反強磁性と超伝導の研究

  小林拓矢, 斉藤洋平, 井原慶彦, 河本充司 日本物理学会講演概要集 68 (1) 2013年
• 18pEB-2 α-(BEDT-TTF)_2RbHg(SCN)_4の^<13>C-NMR(18pEB ET系・超伝導,領域7(分子性固体・有機導体))

  野田 航生, 井原 慶彦, 河本 充司 日本物理学会講演概要集 67 (2) 754 -754 2012年08月24日
• 18aEB-2 圧力下(TMTTF)_2PF_6の電子輸送特性(18aEB 一次元系・パイエルス転移,領域7(分子性固体・有機導体))

  山本 真生, 松永 悟明, 野村 一成, 河本 充司 日本物理学会講演概要集 67 (2) 748 -748 2012年08月24日
• 20pEB-4 κ-(BEDT-TTF)_2Cu_2(CN)_3のラマンスペクトル(20pEB スピン液体(ダイマーモット),領域7(分子性固体・有機導体))

  薬師 久彌, Drozdova Olga, 清水 康弘, 斎藤 軍治, 河本 充司, 山本 貴 日本物理学会講演概要集 67 (2) 789 -789 2012年08月24日
• α‐(BEDT‐TTF)₂RbHg(SCN)₄の¹³C‐NMR

  野田航生, 井原慶彦, 河本充司 日本物理学会講演概要集 67 (2) 754 2012年08月24日 [査読無し][通常論文]
  
• 27pBK-5 κ-(BEDT-TTF)_2Cu(NCS)_2のX線照射効果に関する^<13>C-NMRによる研究(27pBK κ-ET系,領域7(分子性固体・有機導体))

  松本 実子, 加藤 洋生, 桑田 祐希, 河本 充司, 松永 悟明, 野村 一成 日本物理学会講演概要集 67 (1) 929 -929 2012年03月05日
• ¹³C‐NMRによるβ′′‐(BEDT‐TTF)₄[(H₃O)Ga(C₂O₄)₃]・C₆H₅NO₂の超伝導転移直上にみられる異常金属状態の研究

  関春海, 井原慶彦, 河本充司 日本物理学会講演概要集 67 (1) 909 -909 2012年03月05日 [査読無し][通常論文]
  
• 27aBK-9 (TMTTF)_2Xにおける電荷秩序(27aBK 擬一次元系,領域7(分子性固体・有機導体))

  松永 悟明, 岡 雄基, 山本 薫, 河本 充司, 野村 一成, 薬師 久弥 日本物理学会講演概要集 67 (0) 919 -919 2012年 [査読無し][通常論文]
  
• 24aTD-2 ^<13>C-NMRによるβ"-(BEDT-TTF)_4[(H_3O)Ga(C_2O_4)_3]・C_6H_5NO_2の電荷秩序と超伝導の研究(24aTD 有機超伝導(その2),領域7(分子性固体・有機導体))

  関 春海, 井原 慶彦, 河本 充司 日本物理学会講演概要集 66 (2) 887 -887 2011年08月24日
• 23pTG-6 片側^<13>C置換(TMTTF)_2Brの物性(23pTG 擬一次元系,領域7(分子性固体・有機導体))

  劉 洋, 廣瀬 真史, 三沢 雅輝, 河本 充司, 下原 直樹, 野村 一成, 松永 悟明 日本物理学会講演概要集 66 (2) 884 -884 2011年08月24日
• 23pTG-7 圧力下(TMTTF)_2PF_6のスピン密度波相における非線形電気伝導(23pTG 擬一次元系,領域7(分子性固体・有機導体))

  山本 真生, 松永 悟明, 野村 一成, 河本 充司 日本物理学会講演概要集 66 (2) 885 -885 2011年08月24日
• 22pTR-14 圧力下^<13>C-NMRによるκ-(BEDT-TTF)_2Cu[N(CN)_2]Brに関する線幅異常の研究(22pTR モット絶縁体・スピン液体,領域7(分子性固体・有機導体))

  桑田 祐希, 河本 充司 日本物理学会講演概要集 66 (2) 875 -875 2011年08月24日
• ¹³C‐NMRによるβ′′‐(BEDT‐TTF)₄[(H₃O)Ga(C₂O₄)₃]・C₆H₅NO₂の電荷秩序と超伝導の研究

  関春海, 井原慶彦, 河本充司 日本物理学会講演概要集 66 (2) 887 2011年08月24日 [査読無し][通常論文]
  
• 24aTD-1 部分重水素化κ-(BEDT-TTF-d[n,n])_2Cu[N(CN)_2]Brの超伝導ギャップ3 : STM分光(24aTD 有機超伝導(その2),領域7(分子性固体・有機導体))

  岡 雄基, 阿部 良太, 延兼 啓純, 松永 悟明, 野村 一成, 市村 晃一, 河本 充司 日本物理学会講演概要集 66 (2) 887 -887 2011年08月24日 [査読無し][通常論文]
  
• 部分重水素化κ‐(BEDT‐TTF‐d[n,n])₂Cu[N(CN₂)]Brの超伝導ギャップ 3:STM分光

  岡雄基, 阿部良太, 延兼啓純, 松永悟明, 野村一成, 市村晃一, 河本充司 日本物理学会講演概要集 66 (2) 887 2011年08月24日 [査読無し][通常論文]
  
• 25aTA-6 β"-(BEDT-TTF)_3Cl_2・2H_2Oの単結晶^<13>C-NMR(25aTA 電荷秩序・非線形伝導,領域7(分子性固体・有機導体))

  永田 真斗, 河本 充司, 谷口 弘三 日本物理学会講演概要集 66 (1) 843 -843 2011年03月03日
• 部分重水素化κ‐(BEDT‐TTF‐d[3,3])₂Cu[N(CN)₂]Brの超伝導ギャップ:STM分光

  岡雄基, 阿部良太, 延兼啓純, 松永悟明, 野村一成, 市村晃一, 河本充司 日本物理学会講演概要集 66 (1) 863 2011年03月03日 [査読無し][通常論文]
  
• 26aTB-9 部分重水素化κ-(BEDT-TTF-d[3, 3])_2Cu[N(CN)_2]Brの超伝導ギャップ : STM分光(26aTB 有機超伝導,領域7(分子性固体・有機導体))

  岡 雄基, 阿部 良太, 延兼 啓純, 松永 悟明, 野村 一成, 市村 晃一, 河本 充司 日本物理学会講演概要集 66 (1) 863 -863 2011年03月03日 [査読無し][通常論文]
  
• 23pTG-9 (TMTTF)_2SbF_6塩における光学SHGの圧力依存性(23pTG 擬一次元系,領域7(分子性固体・有機導体))

  山本 薫, 河本 充史, 松永 悟明, 野村 一成, 薬師 久弥 日本物理学会講演概要集 66 (0) 885 -885 2011年 [査読無し][通常論文]
  
• 24aRB-4 (TMTTF)_2PF_6のスピン密度波相における誘電率(24aRB 擬一次元物質,領域7(分子性固体・有機導体))

  宮澤 雅臣, 松永 悟明, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 65 (2) 792 -792 2010年08月18日 [査読無し][通常論文]
  
• 24pRB-14 部分重水素化κ-(BEDT-TTF-d[2,2])_2Cu[N(CN)_2]Brの超伝導ギャップ : STM分光(24pRB 領域7,領域8合同 モット転移,領域7(分子性固体・有機導体))

  阿部 良太, 岡 雄基, 松永 悟明, 野村 一成, 市村 晃一, 河本 充司 日本物理学会講演概要集 65 (2) 804 -804 2010年08月18日 [査読無し][通常論文]
  
• 24aRB-6 片側^<13>C置換による(TMTSF)_2PF_6の圧力下^<13>C-NMR(24aRB 擬一次元物質,領域7(分子性固体・有機導体))

  木村 佳敬, 三沢 雅輝, 河本 充司 日本物理学会講演概要集 65 (2) 793 -793 2010年08月18日 [査読無し][通常論文]
  
• 21pGT-8 α-(BEDT-TTF)_2I_3の^<13>C-NMRの磁性状態(21pGT 電荷秩序・誘電性,領域7(分子性固体・有機導体))

  廣瀬 真史, 河本 充司 日本物理学会講演概要集 65 (1) 894 -894 2010年03月01日
• 20pGT-14 片側置換による(TMTSF)_2PF_6の^<13>C-NMR(20pGT 一次元系,領域7(分子性固体・有機導体))

  三沢 雅輝, 木村 佳敬, 河本 充司 日本物理学会講演概要集 65 (1) 863 -863 2010年03月01日 [査読無し][通常論文]
  
• 21pGT-6 α-(BEDT-TTF)_2I_3における電荷秩序ゆらぎと光学電気伝導度(21pGT 電荷秩序・誘電性,領域7(分子性固体・有機導体))

  薬師 久弥, 楽 悦, 山本 薫, 売市 幹大, 比江島 後浩, 河本 充司 日本物理学会講演概要集 65 (0) 893 -893 2010年 [査読無し][通常論文]
  
• 26pRB-8 α'-(BEDT-TTF)_2IBr_2における電荷秩序相転移の同位体効果(26pRB 電荷秩序,領域7(分子性固体・有機導体))

  楽 悦, 売市 幹大, 山本 薫, 薬師 久弥, 河本 充司 日本物理学会講演概要集 65 (0) 835 -835 2010年 [査読無し][通常論文]
  
• 27aYC-3 擬一次元有機導体(TMTTF)_2AsF_6の^<13>C-NMR(TMTTF系/TMTSF系,領域7,分子性固体・有機導体)

  松永 悟明, 下原 直樹, 河本 充司, 野村 一成 日本物理学会講演概要集 64 (2) 767 -767 2009年08月18日
• 27aYC-2 擬一次元有機導体(TMTTF)_2Xのスピン密度波相における誘電率(TMTTF系/TMTSF系,領域7,分子性固体・有機導体)

  宮澤 雅臣, 秋田 知範, 松永 悟明, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 64 (2) 766 -766 2009年08月18日 [査読無し][通常論文]
  
• 27aYC-1 ^<13>C-NMRのための片側^<13>C置換のTMT CF(C=Se,S)分子の作成(TMTTF系/TMTSF系,領域7,分子性固体・有機導体)

  三沢 雅輝, 下原 直樹, 河本 充司, 松永 悟明, 野村 一成 日本物理学会講演概要集 64 (2) 766 -766 2009年08月18日 [査読無し][通常論文]
  
• 30pYF-4 常磁性電荷秩序状態におけるNMRの考察(30pYF α'-ET系,電荷秩序,領域7(分子性固体・有機導体))

  河本 充司, 河合 拓真, 広瀬 真史 日本物理学会講演概要集 64 (1) 863 -863 2009年03月03日
• 30pYF-6 Order-disorder phase transition of α'-(ET)_2IBr_2

  Yue Y., Nakano C., Yamamoto K., Uruichi M., Yakushi K., Kawamoto A. 日本物理学会講演概要集 64 (1) 863 -863 2009年03月03日
• 30pYF-7 α'-(ET)_2IBr_2の高圧下の電子状態(30pYF α'-ET系,電荷秩序,領域7(分子性固体・有機導体))

  薬師 久弥, 楽 悦, 中野 千賀子, 山本 薫, 売市 幹大, ヴォイチェコフスキー R, 井口 眞, 河本 充司 日本物理学会講演概要集 64 (0) 863 -863 2009年 [査読無し][通常論文]
  
• 21pTC-10 (EDT-TTF)_2AuBr_2のSDW相における^1H NMR(21pTC TMTSF/TMTTF系,領域7(分子性固体・有機導体))

  野村 一成, 下原 直樹, 松永 悟明, 河本 充司 日本物理学会講演概要集 63 (2) 757 -757 2008年08月25日
• 22aTC-12 α'-(BEDT-TTF)_2IBr_2単結晶^<13>C-NMR(22aTC α-ET系,領域7(分子性固体・有機導体))

  廣瀬 真史, 河合 拓真, 河本 充司, 熊谷 健一 日本物理学会講演概要集 63 (2) 763 -763 2008年08月25日
• 22aTC-13 Charge-ordering phase transition in α'-(ET)_2IBr_2 studied by infrared, Raman, and far-infrared spectroscopy

  Yue Y., Nakano C., Yamamoto K., Uruichi M., Yakushi K., Kawamoto A. 日本物理学会講演概要集 63 (2) 764 -764 2008年08月25日
• 21pTC-8 擬一次元有機導体(TMTTF)_2Brのスピン密度波相における誘電率(21pTC TMTSF/TMTTF系,領域7(分子性固体・有機導体))

  秋田 知範, 松永 悟明, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 63 (2) 756 -756 2008年08月25日 [査読無し][通常論文]
  
• 22aTC-7 ^<13>C-NMR study of Charge Ordering state in Organic Conductor α-(BEDT-TTF)_2I_3

  河合 択真, 河本 充司, 熊谷 健一 日本物理学会講演概要集 63 (2) 762 -762 2008年08月25日 [査読無し][通常論文]
  
• 23aTC-10 有機物超伝導体κ-(BEDT-TTF)_2Cu(NCS)_2の圧力下単結晶^<13>C-NMR(23aTC κ-ET系,領域7(分子性固体・有機導体))

  板屋 恵, 江頭 由浩, 河本 充司, 熊谷 健一 日本物理学会講演概要集 63 (2) 786 -786 2008年08月25日 [査読無し][通常論文]
  
• 擬一次元有機導体(TMTTF)₂Brにおける磁場誘起スピン密度波転移

  松永悟明, 佐藤健人, 野村一成, 河本充司, 市村晃一, 佐々木孝彦 東北大学金属材料研究所強磁場超伝導材料研究センター年次報告 2007 120-123 2008年06月 [査読無し][通常論文]
  
• 25pTF-7 擬一次元有機導体(TMTTF)_2Xのホール効果(TM系,領域7,分子性固体・有機導体)

  佐藤 健人, 松永 悟明, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 63 (1) 828 -828 2008年02月29日 [査読無し][通常論文]
  
• 22pRB-7 (EDT-TTF)_2AuBr_2のSDW状態における^1H-NMR(ゼロギャップ・1次元系,領域7,分子性固体・有機導体)

  下原 直樹, 間瀬田 拓明, 野村 一成, 河本 充司 日本物理学会講演概要集 62 (2) 875 -875 2007年08月21日
• 22pRB-11 擬一次元有機導体(TMTTF)_2Brのホール効果II(ゼロギャップ・1次元系,領域7,分子性固体・有機導体)

  佐藤 健人, 松永 悟明, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 62 (2) 876 -876 2007年08月21日 [査読無し][通常論文]
  
• 18aRA-7 β'-(BEDSe-TTF)_2X(X=ICl_2, IBr_2)の超高圧下物性(高圧物性・磁性(β,β',β"型塩),領域7,分子性固体・有機導体)

  小松 宏彰, 片山 和弘, 谷口 弘三, 佐藤 一彦, 河本 充司, 辺土 正人, 上床 美也 日本物理学会講演概要集 62 (1) 804 -804 2007年02月28日
• 18aRA-9 β'-(BEDT-TTF)ICl_2の圧力下^<13>C-NMR II(高圧物性・磁性(β,β',β"型塩),領域7,分子性固体・有機導体)

  河本 充司, 江頭 由浩, 熊谷 健一 日本物理学会講演概要集 62 (1) 805 -805 2007年02月28日
• 18pRA-5 部分重水素化κ-(BEDT-TTF-d[2,2])_2Cu[N(CN)_2]BrのSTM分光(κ型塩,領域7,分子性固体・有機導体)

  村岡 竜二, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 62 (1) 812 -812 2007年02月28日 [査読無し][通常論文]
  
• 18pRA-4 κ-(BEDT-TTF)_2Cu[N(CN)_2]Brの側面STS(κ型塩,領域7,分子性固体・有機導体)

  高見 信, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 62 (1) 812 -812 2007年02月28日 [査読無し][通常論文]
  
• 19pRJ-11 擬一次元有機導体(TMTTF)_2Brのホール効果(TMTTF/TMTSF,領域7,分子性固体・有機導体)

  佐藤 健人, 松永 悟明, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 62 (1) 837 -837 2007年02月28日 [査読無し][通常論文]
  
• 実験ノート 市販のFPGAボードを使ったUSB接続NMRパルスジェネレータ

  豊田 朋憲, 河本 充司 固体物理 41 (12) 899 -908 2006年12月
• 23pYF-13 擬一次元有機導体(EDT-TTF)_2AuBr_2の金属-絶縁体転移(23pYF TMTSF/TMTTF系,領域7(分子性固体・有機導体))

  佐藤 健人, 松永 悟明, 野村 一成, 河本 充司 日本物理学会講演概要集 61 (2) 673 -673 2006年08月18日
• 23aYB-4 β'-(BEDT-TTF)_2ICl_2の単結晶^<13>C-NMR(23aYB 金属-絶縁体転移,強相関系,領域7(分子性固体・有機導体))

  江頭 由浩, 今井 優樹, 河本 充司, 熊谷 健一 日本物理学会講演概要集 61 (2) 659 -659 2006年08月18日
• 27aRB-5 β'-(BEDT-TTF)(TCNQ)の赤外反射スペクトルと高圧下^<13>C-NMR(27aRB ET系(β系,κ系,高圧物性),領域7(分子性固体・有機導体))

  河本 充司, 江頭 由浩, 小倉 崇, 熊谷 健一, 山本 薫, 薬師 久弥 日本物理学会講演概要集 61 (0) 801 -801 2006年 [査読無し][通常論文]
  
• 19aWB-12 (BEDT-TTF)(TCNQ)の単結晶^<13>C-NMR(ET塩(κ他),領域7(分子性固体・有機導体))

  江頭 由浩, 河本 充司, 熊谷 健一 日本物理学会講演概要集 60 (2) 672 -672 2005年08月19日
• 24aYL-2 β'-(BEDT-TTF)_2ICl_2の大型単結晶育成とその評価(ET-ICl_2, 超高圧力等,領域7(分子性固体・有機導体))

  谷口 弘三, 佐藤 亮介, 佐藤 一彦, 河本 充司, 岡本 博之, 小林 拓男, 水野 薫 日本物理学会講演概要集 60 (1) 770 -770 2005年03月04日
• 24aYL-1 単結晶中性子回折法による有機導体β'-ET_2ICl_2の磁気秩序とπ電子密度の観測(ET-ICl_2, 超高圧力等,領域7(分子性固体・有機導体))

  松永 篤, 小宮山 聡, 渡邊 真史, 野田 幸男, 谷口 弘三, 河本 充司, 上床 美也 日本物理学会講演概要集 60 (1) 770 -770 2005年03月04日
• 24aYL-7 NMRでみたβ'-(BEDT-TTF)_2ICl_2の磁気転移(ET-ICl_2, 超高圧力等,領域7(分子性固体・有機導体))

  宮川 和也, 小柳 廣継, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 60 (1) 771 -771 2005年03月04日
• 24aYL-6 μSRによるβ'-(BEDT-TTF)_2ICl_2の磁性研究(ET-ICl_2, 超高圧力等,領域7(分子性固体・有機導体))

  佐藤 一彦, 谷口 弘三, 河本 充司, 髭本 亘, 西山 樟生 日本物理学会講演概要集 60 (1) 771 -771 2005年03月04日
• 27aYL-7 κ-(BEDT-TTF)_2Ag(CN)_2H_2Oの低温熱容量(超伝導, κ, β-ET塩等,領域7(分子性固体・有機導体))

  石川 智史, 中澤 康浩, 河本 充司, 小國 正晴 日本物理学会講演概要集 60 (1) 817 -817 2005年03月04日
• 27aYL-3 κ-(BEDT-TTF)_2Cu_2(CN)_3の圧力下^<13>C-NMR(超伝導, κ, β-ET塩等,領域7(分子性固体・有機導体))

  河本 充司, 本間 洋祐, 熊谷 健一 日本物理学会講演概要集 60 (1) 816 -816 2005年03月04日
• 24aYK-3 擬1次元有機導体(TMTTF)_2Brの電荷局在状態における^<13>C-NMR(TMTCF塩, 1D理論,領域7(分子性固体・有機導体))

  鍵和田 淳, 間瀬田 拓明, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 60 (1) 767 -767 2005年03月04日 [査読無し][通常論文]
  
• 13pWE-2 中性子線回折法による有機導体β'-(BEDT-TTF)_2ICl_2 の単結晶構造解析(ET 塩 : β・β´・β"・θ他, 領域 7)

  松永 篤, 小宮山 聰, 渡邉 真史, 野田 幸男, 上床 美也, 河本 充司, 谷口 弘三 日本物理学会講演概要集 59 (2) 752 -752 2004年08月25日
• 13pWE-14 三角格子θ-(BEDT-TTF)_2CsZn(SCN)_4 の低温電子状態(ET 塩 : β・β´・β"・θ他, 領域 7)

  児玉 一宗, 大能 和人, 宮川 和也, 鹿野田 一司, 河本 充司 日本物理学会講演概要集 59 (2) 755 -755 2004年08月25日
• 13pWE-8 (BEDT-TTF)_3Cl_2・2H_2O の ^<13>C-NMR(ET 塩 : β・β´・β"・θ他, 領域 7)

  小倉 崇, 河本 充司, 熊谷 健一, 谷口 弘三 日本物理学会講演概要集 59 (2) 754 -754 2004年08月25日
• 15aWH-10 κ-(ET)_2Cu_2(CN)_3 及びκ-(ET)_2Cu[N(CN)_2]Cl のラマンスペクトル(ET 塩 : к型他, 領域 7)

  Drozdova O., 薬師 久弥, 清水 康弘, 鹿野田 一司, 齋藤 軍治, 河本 充司 日本物理学会講演概要集 59 (2) 778 -778 2004年08月25日
• 15aWH-5 二量体型κ-(BEDT-TTF)_2X 塩の超伝導相内におけるγの挙動(ET 塩 : к型他, 領域 7)

  石川 哲史, 中澤 康浩, 河本 充司, 小國 正晴 日本物理学会講演概要集 59 (2) 777 -777 2004年08月25日
• 29pWL-4 β"-(ET)_3X_2の振動分光学的研究(ET塩・dmit系)(領域7)

  山本 貴, 薬師 久弥, 河本 充司 日本物理学会講演概要集 59 (1) 858 -858 2004年03月03日
• 27aWL-10 κ-(BEDT-TTF)_<2-x>(BEDS-TTF)_xCu[N(CN)_2]Brの^<13>C-NMR(ET塩(κ型))(領域7)

  河本 充司, 佐々木 潤, 熊谷 健一 日本物理学会講演概要集 59 (1) 825 -825 2004年03月03日
• 27pWL-11 θ-(BEDT-TTF)_2I_3の^<13>C NMR(ET塩(α・β・θ型))(領域7)

  宮川 和也, 鹿野田 一司, 田村 雅史, 河本 充司 日本物理学会講演概要集 59 (1) 831 -831 2004年03月03日
• 27pWL-14 ^<13>Cサイトにおける三角格子θ-(BEDT-TTF)_2CsZn(SCN)_4のT_2測定(ET塩(α・β・θ型))(領域7)

  児玉 一宗, 大能 和人, 宮川 和也, 鹿野田 一司, 河本 充司 日本物理学会講演概要集 59 (1) 832 -832 2004年03月03日
• 27pWL-13 θ-(BEDT-TTF)_2RbZn(SCN)_4における電荷秩序と電荷グラスの競合(ET塩(α・β・θ型))(領域7)

  大能 和人, 宮川 和也, 鹿野田 一司, 河本 充司 日本物理学会講演概要集 59 (1) 832 -832 2004年03月03日
• 27aWL-3 κ-(BEDT-TTF)_2Cu[N(CN)_2]BrのSTM分光III(ET塩(κ型))(領域7)

  市村 晃一, 東 真也, 野村 一成, 河本 充司 日本物理学会講演概要集 59 (1) 824 -824 2004年03月03日 [査読無し][通常論文]
  
• 13pWE-12 赤外・ラマン分光法によるθ-(ET)_2CsZn(SCN)_4 の電子状態の研究(ET 塩 : β・β´・β"・θ他, 領域 7)

  鈴木 研二, 山本 薫, 薬師 久弥, 河本 充司 日本物理学会講演概要集 59 (0) 755 -755 2004年 [査読無し][通常論文]
  
• 21aXE-13 κ-(BEDT-TTF)_2X 周辺物質の ^<13>C-NMR

  本間 洋佑, 河本 充司, 熊谷 健一 日本物理学会講演概要集 58 (2) 731 -731 2003年08月15日
• 21aXE-6 κ-(BEDT-TTF)_2Cu[N(CN)_2]Br の低温相の冷却速度依存性

  松永 悟明, 山下 勝美, 山下 真人, 河本 充司, 野村 一成 日本物理学会講演概要集 58 (2) 730 -730 2003年08月15日
• 20aXE-6 NMR で見たθ-(BEDT-TTF)_2RbZn(SCN)_4 の電荷秩序/非秩序状態の動的性質

  大能 和人, 宮川 和也, 鹿野田 一司, 河本 充司 日本物理学会講演概要集 58 (2) 720 -720 2003年08月15日
• 実験ノート 既存のホモダイン受信システムにマッチするNMR用QPSKパルスモジュレータの製作

  河本 充司, 山下 真人 固体物理 37 (11) 831 -838 2002年11月
• 8pSD-1 部分重水素化κ-(BEDT-TTF)2Cu[N(CN)2]BrのMR(II)(ET系(κ系)・超伝導,領域7)

  沖津 信一, 山下 真人, 河本 充司, 熊谷 健一 日本物理学会講演概要集 57 (2) 710 -710 2002年08月13日
• 8pSD-2 超伝導体κ-(BEDT-TTF)2Cu(NCS)2を用いた平行磁場およびその近傍における磁束状態のMRによる研究(ET系(κ系)・超伝導,領域7)

  宮川 和也, 妹尾 敦喜, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 57 (2) 710 -710 2002年08月13日
• 9aSD-9 A Raman Study of the charge ordering in α-(BEDT-TTF)2I3 at high pressure

  WOJCIECHOWSKI Roman, YAMAMOTO Kaoru, YAKUSHI Kyuya, KAWAMOTO Atsushi 日本物理学会講演概要集 57 (2) 717 -717 2002年08月13日
• π-d相互作用系有機無機ハイブリッドシステムにおけるNMRによる局所磁化率分割とバンド磁化率分割

  河本 充司, 宮川 和也, 鹿野田 一司 固体物理 37 (5) 326 -334 2002年05月
• 26pXM-3 κ-(BEDT-TTF)_2Cu[N(CN)_2]BrのSTM分光 II(26pXM ET錯体類(κ系),領域7(分子性固体・有機導体分野))

  鈴木 一裕, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 57 (1) 793 -793 2002年03月01日
• 26pXM-7 κ-(ET)_2Cu[N(CN)_2]Brの擬ギャップ的ふるまいの磁場依存性(26pXM ET錯体類(κ系),領域7(分子性固体・有機導体分野))

  松本 充功, 宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 57 (1) 794 -794 2002年03月01日
• 25pYL-7 π-d有機結晶系におけるバンド選択NMR(25pYL 領域3,領域7,領域8合同シンポジウム 主題:核磁気共鳴による物性研究:最近の展開と新領域の開拓,領域3(磁性,磁気共鳴分野))

  河本 充司 日本物理学会講演概要集 57 (1) 432 -432 2002年03月01日
• 19pWF-12 の超低温域における^<13>C-NMR

  古田 旭, 宮川 和也, 谷口 弘三, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 56 (2) 705 -705 2001年09月03日
• 19pWF-11 κ(d[4,4]-ET)_2Cu[N(CN)_2]Brの^<13>C-NMRの磁場依存性

  松本 充功, 小西 邦昭, 宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 56 (2) 704 -704 2001年09月03日
• 19pWF-2 κ-(BEDT-TTF)_2Cu[N(CN)_2]Brの置換効果

  佐々木 潤, 山下 真人, 河本 充司, 熊谷 健 日本物理学会講演概要集 56 (2) 702 -702 2001年09月03日
• 18aWF-10 (BEDT-TTF)(ClMeTCNQ)のNMR

  宮川 和也, 鹿野田 一司, 長谷川 達生, 河本 充司 日本物理学会講演概要集 56 (2) 690 -690 2001年09月03日
• 17aWF-9 α-(BEDT-TTF)_2NH_4Hg(SeCN)_4の構造と物性

  河本 充司, 山下 真人, 熊谷 健一, 中尾 朗子, 福田 豊, 鹿野 田一司, 谷口 弘三 日本物理学会講演概要集 56 (2) 677 -677 2001年09月03日
• 17aWE-8 圧力下におけるα-(BEDT-TTF)_2I_3の電子状態

  久保 徳明, 鷹野 芳樹, 開 康一, 高橋 利宏, 山本 浩史, 中村 敏和, 河本 充司, 熊谷 健一 日本物理学会講演概要集 56 (2) 676 -676 2001年09月03日
• 28pWB-10 κ-(d[4,4]-BEDT-TTF)_2Cu[N(CN)_2]Bのモット転移近傍における高磁場下^<13>-NMR

  小西 邦昭, 松本 充功, 宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 56 (1) 753 -753 2001年03月09日
• 28pWB-15 (EDTDM)_2Xの^<13>C NMR

  宮川 和也, 鹿野田 一司, 岡部 一毅, 宮崎 章, 榎 敏明, 河本 充司 日本物理学会講演概要集 56 (1) 754 -754 2001年03月09日
• 28pWB-9 κ-(BEDT-TTF)_2Cu(NCS)_2の超伝導状態のNMR

  木許 誠一郎, 宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 56 (1) 753 -753 2001年03月09日
• 28pWB-8 部分重水素化したκ-(BEDT-TTF)_2Cu[N(CN)_2]Br-1

  山下 真人, 河本 充司, 熊谷 健一 日本物理学会講演概要集 56 (1) 752 -752 2001年03月09日
• 28pWB-6 κ-(BEDT-TTF)_2Cu[N(CN)_2]BrのSTM分光

  鈴木 一裕, 市村 晃一, 野村 一成, 河本 充司 日本物理学会講演概要集 56 (1) 2001年03月09日 [査読無し][通常論文]
  
• 23pYG-4 Raman spectra of κ-(BEDT-TTF)_2Cu[N(CN)_2]Br and its deuterated analogues

  Maksimuk M., 薬師 久弥, 谷口 弘三, 鹿野田 一司, 河本 充司 日本物理学会講演概要集 55 (2) 715 -715 2000年09月10日
• 23pYG-5 κ-(d[2,2]-ET)_2Cu[N(CN)_2]Brのモット転移近傍における超伝導 : 絶縁体転移の^1H-NMR

  松本 充功, 宮川 和也, 谷口 弘三, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 55 (2) 715 -715 2000年09月10日
• 25aZJ-12 NMRで観測したκ-(BEDT-TTF)_2Cu(NCS)_2の平行磁場下混合状態

  内田 和男, 宮川 和也, 谷口 弘三, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 55 (1) 553 -553 2000年03月10日
• 24pR-2 Raman-active C=C vibrations of κ-(BEDT-TTF)_2Cu[N(CN)_2]Br and its deuterated analogues

  Maksimuk M., 薬師 久弥, 谷口 弘三, 鹿野田 一司, 河本 充司 日本物理学会講演概要集 55 (1) 729 -729 2000年03月10日
• 24pR-11 (BEDT-TTF)_4Hg_<2.78>Cl_8の^<13>C NMR

  宮川 和也, 谷口 弘三, 河本 充司, 布施 琢也, 鹿野田 一司 日本物理学会講演概要集 55 (1) 731 -731 2000年03月10日
• 23aYG-5 θ-(BEDT-TTF)_2RbZn(SCN)_4の振動スペクトルの帰属と電荷配列

  山本 薫, 薬師 久弥, 宮川 和也, 鹿野田 一司, 河本 充司 日本物理学会講演概要集 55 (0) 708 -708 2000年 [査読無し][通常論文]
  
• 27aYP-7 Mott転移近傍の有機伝導体における磁場誘起超伝導-絶縁体転移

  谷口 弘三, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 54 (2) 577 -577 1999年09月03日
• 25pE-6 ^<13>C-NMRで観測したκ-(BEDT-TTF)_2Cu(NCS)_2の超伝導状態

  内田 和男, 富川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 54 (2) 747 -747 1999年09月03日
• 25aE-8 α-(BEDT-TTF)_2RbHg(SCN)_4における^<13>C NMRのT_1およびスペクトルの角度依存性

  宮本 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 54 (2) 741 -741 1999年09月03日
• 28p-D-2 有機強相関系のNMR

  鹿野田 一司, 宮川 和也, 河本 充司, 開 康一 日本物理学会講演概要集 54 (1) 498 -499 1999年03月15日
• 27p-N-10 κ-(BEDT-TTF)_2Cu[N(CN)_2]Clの低温における磁気構造

  内田 和男, 宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 53 (2) 316 -316 1998年09月05日
• 27p-N-5 部分重水素化したκ-(BEDT-TTF)_2Cu[N(CN)_2]Brの物性 I

  河本 充司, 谷口 弘三, 鹿野田 一司 日本物理学会講演概要集 53 (2) 315 -315 1998年09月05日
• 27a-N-10 θ-(BEDT-TTF)_2RbZn(SCN)_4のNMR II

  宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 53 (2) 309 -309 1998年09月05日
• 30a-YP-4 (DMe-DCNQI)_2Cuの金属相の^<13>C,^<15>N-NMR

  河本 充司, 宮川 和也, 鹿野田 一司 日本物理学会講演概要集 53 (1) 225 -225 1998年03月10日
• 30p-YP-12 θ-(BEDT-TTF)_2RbZn(SCN)_4のNMR I

  宮川 和也, 鹿野田 一司, 河本 充司 日本物理学会講演概要集 53 (1) 233 -233 1998年03月10日
• 6p-C-4 (DMe-DCNQI)_2Cuの絶縁体相のNMR

  河本 充司, 宮川 和也, 鹿野田 一司 日本物理学会講演概要集 52 (2) 282 -282 1997年09月16日
• 7a-D-2 α-(BEDT-TTF)_2MHg(SCN)_4の低温相の^<13>C-NMR

  宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 52 (2) 291 -291 1997年09月16日
• 8a-C-10 β'-(BEDT-TTF)_2ICl_2の^<13>C-NMR II

  鹿野田 一司, 宮川 和也, 河本 充司 日本物理学会講演概要集 52 (2) 300 -300 1997年09月16日
• 29p-C-1 Mott絶縁体β'-(BEDT-TTF)_2ICl_2のNMR I

  宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集 52 (1) 275 -275 1997年03月17日
• κ-(BEDT-TTF)_2Xの絶縁相のNMR II

  宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1996 (2) 425 -425 1996年09月13日
• 異種核サイトNMRでみたκ-(BEDT-TTF)_2Xのボルテックス状態

  鹿野田 一司, 宮川 和也, 河本 充司 日本物理学会講演概要集. 秋の分科会 1996 (2) 441 -441 1996年09月13日
• β-(BEDT-TTF)_2I_3のアニール効果 : NMRと磁化率

  河本 充司, 宮川 和也, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1996 (2) 436 -436 1996年09月13日
• 3p-B-8 β-(BEDT-TTF)_2X の NMR III

  宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集. 年会 51 (2) 401 -401 1996年03月15日
• 3p-B-9 κ-(BEDT-TTF)_2絶縁相のNMR

  河本 充司, 宮川 和也, 鹿野田 一司 日本物理学会講演概要集. 年会 51 (2) 402 -402 1996年03月15日
• 29p-K-2 κ-(BEDT-TTF)_2Cu[N(CN)_2]Brの超伝導状態のNMR

  鹿野田 一司, 宮川 和也, 河本 充司, 中澤 康浩 日本物理学会講演概要集. 秋の分科会 1995 (2) 400 -400 1995年09月12日
• 29p-K-1 κ-(BEDT-TTF)_2Cu[N(CN)_2]Br塩のD置換体の^<13>C-NMR

  河本 充司, 宮川 和也, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1995 (2) 399 -399 1995年09月12日
• 29a-K-11 β-(BEDT-TTF)_2XのNMR I

  宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1995 (2) 392 -392 1995年09月12日
• 29a-K-12 β-(BEDT-TTF)_2XのNMR II : アニール効果

  宮川 和也, 河本 充司, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1995 (2) 392 -392 1995年09月12日
• 29p-YS-9 DCNQI系のNMRIII

  河本 充司, 宮川 和也, 中澤 康浩, 鹿野田 一司 日本物理学会講演概要集. 年会 50 (2) 387 -387 1995年03月16日
• 31a-YS-9 (BEDT-TTF)(TCNQ)のNMRII

  清水 彰子, 宮川 和也, 河本 充司, 中澤 康浩, 鹿野田 一司 日本物理学会講演概要集. 年会 50 (2) 417 -417 1995年03月16日
• 29a-YS-11 k-(BEDT-TTF)_2XのNMR V

  宮川 和也, 河本 充司, 中澤 康浩, 鹿野田 一司 日本物理学会講演概要集. 年会 50 (2) 376 -376 1995年03月16日
• 31p-YS-13 α-(BEDT-TTF)_2MHg(SCN)_4の低温比熱 III

  中澤 康浩, 河本 充司, 鹿野田 一司 日本物理学会講演概要集. 年会 50 (2) 431 -431 1995年03月16日
• 31p-YS-10 α-(BEDT-TTF)_2MHg(SCN)_4のNMR IV

  鹿野田 一司, 宮川 和也, 河本 充司, 中澤 康浩 日本物理学会講演概要集. 年会 50 (2) 430 -430 1995年03月16日
• 4a-X-5 Laの高温・高圧下におけるリエントラント相転移

  岡部 直子, 浜谷 望, 河本 充司, 山片 正明, 八木 健彦, 遊佐 斉, 下村 理 日本物理学会講演概要集. 秋の分科会 1994 (2) 457 -457 1994年08月16日
• 3p-S-12 (BEDT-TTF)(TCNQ)のNMR-I

  宮川 和也, 河本 充司, 中澤 康浩, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1994 (2) 280 -280 1994年08月16日
• 4a-S-7 (DMe-DCNQI)_2CuのNMRII

  河本 充司, 宮川 和也, 中澤 康浩, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1994 (2) 290 -290 1994年08月16日
• 3a-S-8 α-(BEDT-TTF)_2MHg(SCN)_4のNMR-III

  宮川 和也, 河本 充司, 中澤 康浩, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1994 (2) 272 -272 1994年08月16日
• 29p-YG-8 ランタン、プラセオジム、ネオジムの高圧力下の結晶構造相転移

  浜谷 望, 岡部 直子, 河本 充司, 川田 肇, 藤井 保彦, 八木 健彦 日本物理学会講演概要集. 年会 49 (3) 260 -260 1994年03月16日
• 31a-YJ-10 α-(BEDT-TTF)_2NH_4Hg(SCN)_4の超伝導転移の特異性

  佐藤 博彦, 中澤 康浩, 河本 充司, 加藤 清則, 鹿野田 一司 日本物理学会講演概要集. 年会 49 (2) 337 -337 1994年03月16日
• 31a-YJ-6 α-(BEDT-TTF)_2MHg(SCN)_4の^<13>C-NMR II

  宮川 和也, 河本 充司, 中澤 康浩, 鹿野田 一司 日本物理学会講演概要集. 年会 49 (2) 335 -335 1994年03月16日
• 31a-YJ-5 α-(BEDT-TTF)_2MHg(SCN)_4の熱力学的性質

  中澤 康浩, 河本 充司, 佐藤 博彦, 鹿野田 一司 日本物理学会講演概要集. 年会 49 (2) 334 -334 1994年03月16日
• 28a-YJ-12 (DMe-DCNQI)_2CuのNMR I

  鹿野田 一司, 河本 充司, 宮川 和也, 中澤 康浩 日本物理学会講演概要集. 年会 49 (2) 282 -282 1994年03月16日
• 31p-YJ-9 κ-(BEDT-TTF)_2X の NMR III

  河本 充司, 宮川 和也, 中澤 康浩, 佐藤 博彦, 鹿野田 一司 日本物理学会講演概要集. 年会 49 (2) 349 -349 1994年03月16日
• 13p-C-3 α-(BEDT-TTF)_2NH_4Hg(SCN)_4の複素帯磁率

  鹿野田 一司, 中澤 康浩, 河本 充司, 加藤 清則 日本物理学会講演概要集. 秋の分科会 1993 (2) 386 -386 1993年09月20日
• 12p-C-9 κ-(BEDT-TTF)_2Xの^<13>C-NMR II

  宮川 和也, 河本 充司, 中澤 康浩, 佐藤 博彦, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1993 (2) 367 -367 1993年09月20日
• 12p-C-8 κ-(BEDT-TTF)_2Xの^<13>CNMR-I

  河本 充司, 宮川 和也, 中澤 康浩, 佐藤 博彦, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1993 (2) 366 -366 1993年09月20日
• 12a-C-8 k-(BMDT-TTF)_2Au(CN)_2の^1H-NMR

  宮川 和也, 河本 充司, 森 健彦, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1993 (2) 361 -361 1993年09月20日
• 13p-C-5 α-(BEDT-TTF)_2MHg(SCN)_4の^<13>C-NMR I

  鹿野田 一司, 宮川 和也, 河本 充司, 中澤 康浩 日本物理学会講演概要集. 秋の分科会 1993 (2) 387 -387 1993年09月20日
• 13p-C-4 α-ET_2NH_4Hg(SCN)_4の磁場中抵抗

  佐藤 博彦, 中澤 康浩, 河本 充司, 加藤 清則, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1993 (2) 386 -386 1993年09月20日
• 12p-C-11 κ-(BEDT-TTF)2Xの複素帯磁率 I

  鹿野田 一司, 中澤 康浩, 河本 充司 日本物理学会講演概要集. 秋の分科会 1993 (2) 368 -368 1993年09月20日
• 13p-C-2 α-ET_2MHg(SCN)_4の低温電気抵抗、帯磁率

  中澤 康浩, 佐藤 博彦, 河本 充司, 加藤 清則, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1993 (2) 385 -385 1993年09月20日
• 13p-C-12 α-ET_2TlHg(SCN)_4の低温電子状態

  佐藤 博彦, 中澤 康浩, 河本 充司, 宮川 和也, 水谷 伸雄, 鹿野田 一司 日本物理学会講演概要集. 秋の分科会 1993 (2) 390 -390 1993年09月20日
• CRYSTAL-STRUCTURE OF AN ALTERNATED STACKING CHARGE-TRANSFER COMPLEX OF 2,7-BIS(METHYLTHIO)-1,6-DITHIAPYRENE (MTDTPY) WITH TETRACYANO-2,6-NAPHTHOQUINODIMETHANE (TNAP)

  J TOYODA, A ODA, MURATA, I, A KAWAMOTO, J TANAKA, K NAKASUJI BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 66 (7) 2115 -2117 1993年07月 [査読無し][通常論文]
   

  The charge-transfer complex of 2,7-bis-(methylthio)-1,6-dithiapyrene (MTDTPY) with tetracyano-2,6-naphthoquinodimethane (TNAP) showed an alternated stacking mode of crystal structure. There are no short intermolecular contacts. The ionicity was estimated to be neutral. based on an analysis of the IR stretching frequency of the CN groups and the transition energy of the charge-transfer band.
• 28p-K-4 κ-(DMET)_2AuBr_2のドハース・ファンアルフェン効果

  鹿野田 一司, 加藤 清則, 河本 充司, 大嶋 孝吉, 高橋 利宏, 菊地 耕一, 斉藤 一弥, 池本 勲 秋の分科会講演予稿集 1992 (2) 376 -376 1992年09月14日
• Exploration of New Cooperative Proton-Electron Transfer (PET) Systems. First Example of Extended Conjugated Quinhydrones: 1,5-Dihalo-2,6-naphthoquinhydrones

  Kazuhiro Nakasuji, Kenichi Sugiura, Toshikazu Kitagawa, Jiro Toyoda, Hiroshi Okamoto, Kaoru Okaniwa, Tadaoki Mitani, Hiroshi Yamamoto, Ichiro Murata, Atsushi Kawamoto, Jiro Tanaka Journal of the American Chemical Society 113 (5) 1862 -1864 1991年 [査読無し][通常論文]
  
• CRYSTAL-STRUCTURE OF 1-2 CHARGE-TRANSFER COMPLEX OF 2,7-BIS(METHYLTHIO)-1,6-DITHIAPYRENE (MTDTPY) AND TETRAHYDROBARRELENO-TETRACYANOQUINODIMETHANE (THBTCNQ)

  K NAKASUJI, M SASAKI, MURATA, I, A KAWAMOTO, J TANAKA BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 61 (12) 4461 -4463 1988年12月 [査読無し][通常論文]
  

共同研究・競争的資金等の研究課題

• 電荷不均化を持つ新奇有機超伝導体の超伝導の対称性とＦＦＬＯ状態の探索

  文部科学省：科学研究費補助金(基盤研究(C))

  研究期間 : 2012年 -2014年 

  代表者 : 河本 充司, 井原 慶彦

   

  有機超伝導体β”-(BEDT-TTF)4 [(H3O)Ga(C2O4)3C6H5NO2は、常磁性相で電荷不均一が見つかっており、理論から提唱されている電荷の揺らぎを介した新しいタイプの有機超伝導体である可能性が示唆される。この電荷の自由度に加えパウリ限界を超える上部臨界磁場が実験で報告されている。昨年度は、(1) 秩序パラメータの対称性が、スピンシングレットのd波超伝導であることを明らかにしたが、本年度は、昨年度発見した超伝導直上の異常に関して常磁性電子状態の特性を片側置換13C-NMRの手法を用いて調べた。β''-Ga塩の高磁場NMR測定をグルノーブル（フランス）の高磁場実験施設との共同研究で行った。高磁場の実験から低磁場では、10K以下で線幅の増大として観測されていたピークは、２本のピークに分離していることがあきらかになった。この２本のピークの角度依存の測定より、電荷のリッチなサイトとプアなサイトであることが定量的に解析された。電荷は、 それぞれ0.6e と 0.13eと見積もられた。また、これらのピークの強度比から、サイトの比が単純な1:1の分離ではなく 3:1であることがわかり、このことから電荷分離のパターンに関して考察を行った。これらの大きな電荷の分離は、超伝導状態においても観測された。電荷の分離と超伝導の共存するが、実証された例は、有機超伝導体では初めての例であり、電荷付近化がこの物質の高いHc2と関連していると考えられる。
• 片側13C置換によるTMTSF塩の異常な超伝導状態におけるNMR

  文部科学省：科学研究費補助金(基盤研究(C))

  研究期間 : 2008年 -2010年 

  代表者 : 河本 充司

   

  (TMTCF)_2X,X=S,Se,で表記される塩は、擬1次元電子としての特徴を持っておりその低次元物性およびTMTSF塩において観測された超伝導などに興味が持たれ研究されて詳細に研究されてきた。近年のこの塩における超伝導の研究においてPauli限界を超える高いHc2や三重項超伝導など通常の超伝導とは異なる性質が報告されている。このような新奇な電子物性を微視的な観点から明らかにするためにNMRは重要なツールである。しかし、Pakeダブレットの問題等を克服するために中心C=C結合の片側のみを^<13>Cに置換することが望まれる。そこでこの同位体置換を可能にする新たなTMTSFの合成ルートを確立し、(TMTSF)_2X塩の超微細結合テンソルを決定した。このデータを用いて、(TMTSF)_2PF_6塩の低温SDW sub phaseにおける部分的な整合状態を明らかにし、また(TMTSF)_2PF_6塩の超伝導直上の非Fermi液体状態の原因が、SDW揺らぎが原因であること、そしてこの揺らぎが超伝導の発現に密接に関係していることを明らかにした。
• 重水素置換NMRによる電荷ダイナミクスの研究

  文部科学省：科学研究費補助金(基盤研究(C))

  研究期間 : 2006年 -2007年 

  代表者 : 河本 充司

   

  複雑液体や、機能性材料の研究において電荷のダイナミクスを研究することは、誘電物性やその起源を研究する手段として重要である。水素結合を含む水やアルコールにおける分子運動などは、生体における水の役割の解明する上で重要であるが、その緩和現象はタイムスケールによりいくつかの階層構造からなり複雑である。また導電性有機物において近年、分子運動のタイムスケールの非常に遅い緩和現象が発見されそのダイナミクスの解明が進んでいる。速いダイナミクスを光学測定、非常に遅いダイナミクスは誘電測定にたよるのが現状であるが、磁気共鳴のタイムスケールでの研究は遅いダイナミクスの研究に相補的な情報を提供できる。磁性体および金属の物性研究においてNMRは、スピンの静的な性質だけでなく動的な性質を測定できる非常に重要な実験手段である。磁性研究における花形的存在であるNMRも誘電測定への応用となると、以下にあげる欠点により研究例はあるが磁性体に関するNMRのように決定的な実験手段とはなっていない。これらの欠点を克服する新たな誘電物性の測定手段としての磁気共鳴の方法を確立することをめざし、重水素、水素2つのプローブを測定して情報を引き出すことを試みた。目的物質の(TTF-d)(TCNQ一h)と(TTF-h)(TCNQ-d)体のうち(TTF-d)(TCNQ-h)については、分子の合成および大型単結晶の作成も完了し現在測定を予定している段階でありTCNQ-d体の合成も昨年度末に合成ルートの見通しがたち現在、合成を試みている現状である。
• 圧力下における有機超伝導体の単結晶角度回転13C-NMR

  文部科学省：科学研究費補助金(特定領域研究)

  研究期間 : 2006年 -2007年 

  代表者 : 河本 充司

   

  β'-(BEDT-TTF)ICl_2の超微細結合テンソルと反強磁性モーメントの決定昨年度よりβ'-(BEDT-TTF)塩の圧力下13C-NMRを精力的に行っていた。圧力下超伝導体塩であるβ'-(BEDT-TTF)_2ICl_2の反強磁性相の構造の決定は、その圧力下超伝導のメカニズムを議論する上で重要である。反強磁性相の重要なパラメータである交番磁化の決定には、超微細結合テンソルの非対角項が必要なる。そのため、角度回転NMRによりそれぞれの角度でスペクトルの温度変化を測定しK-xプロットをし、その3軸での角度依存性を決定することにより完全な超微細結合テンソルを決定した。このテンソルを用いて反強磁性相での交番磁化が、ほぼBEDT-TTF二量体あたり1μBであることがわかり、常圧では、Mott絶縁体であることが明らかになった。また加圧下の反強磁性相は、NMRのスペクトルの構造が変化していること、常磁性相でのキュリー定数の値が減少していること、転移温度が圧力とともに上昇することが圧力下13C-NMRによりわかった。これらの現象は、Mott絶縁体描像、バンド描像のどちらの立場にたっても完全に説明することはできないことより今後のこの圧力下状態に対する理論的な発展が待たれるところである。また類縁物質であるβ'-(BEDT-TTF)(TCNQ)のの電荷移動量について知見をえるために分子科学研究所の薬師グループとの共同研究で、赤外スペクトルを測定し、電荷移動量が0.5でありTCNQがMott dimer絶縁体であるこを示した。さらに単結晶13C-NMRの圧力変化の測定も行いこの物質が圧力下で金属化するが超伝導を示さない要因としてNMRシフトの異常よりTCNQとの交換相互作用の存在を明らかにし、圧力下磁場有機超伝導の可能性を提示した。
• 高圧下における有機超伝導体の単結晶角度回転^<13>C-NMR

  文部科学省：科学研究費補助金(特定領域研究)

  研究期間 : 2004年 -2005年 

  代表者 : 河本 充司

   

  昨年度にひきつづき、測定対象としては以下示す結晶について有機伝導体の単結晶^<13>C-NMRの圧力測をおこなった。(1)β'-(BEDT-TTF)(TCNQ) この結晶は、超高圧下で有機物最高の超伝導転移温度をもつβ'-(BEDT-TTF)_2ICl_2とBEDT-TTF伝導層が同型の構造をしており、また過去の我々の研究により、常圧においてβ'-(BEDT-TTF)_2ICl_2と同様にBEDT-TTF伝導層が反強磁性が出現することが明らかになっている。圧力下でこの転移温度がどのように変化するか、また反強磁性が生き残るか、という点において圧力下で^<13>C-NMRの測定を行った。その結果8kbarまでは、加圧に従い反強磁性転移温度が上昇するが8kbar以上で急激に減少することが明らかになった。反強磁性転移温度の上昇は系の次元性の変化として理解できる。現在、それ以上の圧力下における電子状態やTCNQ層の磁性の測定を検討している。(2)β"-(BEDT-TTF)_2Cl_3・H_2O この結晶は、β"型という電荷秩序が発現することが知られている伝導層の積層様式を持ってる。また、圧力下でこの物質が超伝導をしめすことより超伝導と電荷揺らぎの相関に興味が持たれる。^<13>C-NMRの圧力変化より、電荷秩序の形成を明らかにし、圧力によりその電荷秩序状態が制御されることをみいだした。
• 部分重水素下における有機超伝導体の超伝導絶縁体近傍における^<13>C-NMR

  文部科学省：科学研究費補助金(基盤研究(C))

  研究期間 : 2002年 -2003年 

  代表者 : 河本 充司

   

  High-Tc酸化物を含む強相関電子系は、反強磁性と超伝導との関連がその超伝導発現メカニズムに重要な役割を示すことが数多くの実験事実、理論的研究により明らかになってきた。また有機超伝導体κ-(BEDT-TTF)_2Xの^<13>C-NMRによる研究でκ-(BEDT-TTF)_2X系も酸化物や重い電子系と同様、反強磁性と超伝導が密接にかかわる強相関電子系であることが示唆されている。さて強相関電子系の共通する特徴として、Tc以上での金属状態が通常のフェルミ液体ではないことが挙げられる。また、超伝導相の近傍に磁性絶縁相が存在する特徴もある。超伝導絶縁体近傍で、状態密度が発散して絶縁体化するのかどうかという点および低温の金属状態がどのような性質なのかは強相関電子系では重要な問題である。この超伝導絶縁体近傍の物性にアプローチする方法としては、そこに位置している適切なモデル物質が必要である。超伝導絶縁体近傍に位置するモデル物質してκ-(BEDT-TTF)_2Cu[N(CN)_2]Brが存在する。BEDT-TTF分子のプロトンを部分的に重水素化することにより、パッキングを密にして等価的に圧力をかけることができる。また酸化物超伝導体とは違いκ-(BEDT-TTF)_2Cu[N(CN)_2]Brは、比較的上部臨界磁場Hc2が小さく磁場で超伝導を壊し、低温状態で金属状態を容易に調べることができる。この超伝導絶縁体近傍の電子状態の状態密度、磁気構造、スピンダイナミクスを部分重水素体のNMRにおいてシステマティックに調べることにより超伝導絶縁体近傍についての電子状態の詳細な知見を得ることを目的とし実験を行った。その結果、超伝導・絶縁体相境界に近づけた場合、超伝導を壊した金属相の状態は、あまり変化しないことが明らかになった。また20K以下で金属・反強磁性絶縁相の相分離が観測され、相境界に近づくにつれて反強磁性絶縁相の割合が増大することがわかった。また、全重水素置換体において伝導面内に平行に磁場をかけた場合、T*において常磁性絶縁体相・金属相の相分離現象が発見された。この相分離現象は、常磁性絶縁体相・金属相間が1次の相転移であることを示唆することと、相転移ラインが、磁場の方向に強く依存することを示唆しており、このκ-(BEDT-TTF)_2Xの電子状態の解明に重要な知見をあたえるものと期待している。
• 分子性機能物質の核磁気共鳴による研究

  文部科学省：科学研究費補助金(奨励研究(A))

  研究期間 : 1998年 -1999年 

  代表者 : 河本 充司

   

  分子性機能物質の核磁気共鳴というテーマで、磁気共鳴用、同位体置換サンプルの合成、また物性用の広幅NMRに適した、NMR,NQRのシステム開発を目的としてプロジェクトを遂行してきた。装置の開発に思った以上に時間がかかったが、何とか、今年度末には高機能汎用パルス発生器、超高速(40MHz 12bit dual channel)AD変換システムの完成ができそうである。現在のところ、ハードウェア単体での性能は当初の目的を達している。今日の測定においては、計算機による測定系の集中管理が必要であり、作成したハードウェアと計算機用のドライバはセットとしてつくらなければその利用価値は少ない。そこでWindows NT/2000でこれらのハードウェアを制御することのできるドライバも合わせて開発した。ハード基板は、分子科学研究所の装置開発室の豊田氏にコンタクトをとれば入手可能であり、またドライバは、Internetを通じて配布の予定で、これにより、広幅NMRを研究者に広く利用、普及してもらえることを考えている。この装置の部分の成果については、豊田氏が、すでに技術研究会等で発表している。また、実際の測定は、装置開発が手間取ったため、既存設備を用いて先行して行うことにした。その中で、分子と金属イオンのhybridの物質であり、その分子のp軌道と金属のd軌道が相互作用して、多彩な物性を発現する(DMe-DCNQI)_2Cuについて^<13>C、^<15>Nの選択的同位体置換NMRでその多彩な物性の発現機構について知見をうることができた。その成果の一部はすでに論文に発表し、また最終報告を投稿予定としている。さらに、強相関系有機超伝導体k-(BEDT-TTF)_2Cu[N(CN)_2]BrにおいてHをD化することによりMott境界をSCANできることを発見して現在その^<13>C置換体の合成に着手ちている次第である。この部分については、今後、研究成果が出るものと期待している。

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