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Master

Affiliation (Master)

  • Faculty of Science　Physics　Quantum Physics

Affiliation (Master)

  • Faculty of Science　Physics　Quantum Physics

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Profile and Settings

Profile and Settings

  • Name (Japanese)

    Matsunaga

  • Name (Kana)

    Noriaki

  • Name

    200901083186745737

Alternate Names

Achievement

Research Interests

  • 強磁場中の電子物性   

Research Areas

  • Natural sciences / Magnetism, superconductivity, and strongly correlated systems

Published Papers

  • Kazuoki Yokoi, Issei Miyazaki, Koichi Ichimura, Satoshi Tanda, Noriaki Matsunaga, Tohru Kurosawa, Migaku Oda
    Solid State Communications 371 115262 - 115262 0038-1098 2023/10 [Refereed][Not invited]
  • Koichi Ichimura, Hiroki Kokubo, Satoshi Tanda, Tohru Kurosawa, Migaku Oda, Hiroki Honma, Noriaki Matsunaga, Kazuto Moribe, Yoshihiko Ihara, Atsushi Kawamoto
    Proceedings of the 29th International Conference on Low Temperature Physics (LT29) 2023/05/22
  • Rikumaru Saito, Youhei Iida, Takuya Kobayashi, Hiromi Taniguchi, Noriaki Matsunaga, Shuhei Fukuoka, Atsushi Kawamoto
    Physical Review B 105 (16) 2022/04/11 [Refereed]
  • Youhei Iida, Masashi Sawada, Yoshiaki Sasaki, Tomoaki Tsuchiya, Takaaki Minamidate, Noriaki Matsunaga, Atsushi Kawamoto, Kazushige Nomura
    Physical Review B 104 (18) 2469-9950 2021/11/04 [Refereed][Not invited]
     
    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.
  • Ryota Yano, Masaki Yoshida, Takahiro Tsunenari, Ayana Sato-Tomita, Shunsuke Nozawa, Youhei Iida, Noriaki Matsunaga, Atsushi Kobayashi, Masako Kato
    Dalton Transactions 50 (25) 8696 - 8703 1477-9226 2021 [Refereed]
     

    The nickel(ii)–chloranilato complex shows reversible vapochromism with changes in dimensionality upon exposure to various vapours and subsequent drying by heating.

  • Shuhei Fukuoka, Takaaki Minamidate, Noriaki Matsunaga, Yoshihiko Ihara, Atsushi Kawamoto
    Journal of the Physical Society of Japan 89 (7) 073704 - 073704 0031-9015 2020/07/15 [Refereed][Not invited]
  • T. Kobayashi, T. Ishikawa, A. Ohnuma, M. Sawada, N. Matsunaga, H. Uehara, A. Kawamoto
    Physical Review Research 2020/04/24 [Refereed][Not invited]
  • Y. Saito, T. Minamidate, A. Kawamoto, N. Matsunaga, K. Nomura
    PHYSICAL REVIEW B 98 205141  2018/10 [Refereed][Not invited]
  • 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) 093705  0031-9015 2018/09 [Refereed][Not invited]
     
    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.
  • Takaaki Minamidate, Hironori Shindo, Yoshihiko Ihara, Atsushi Kawamoto, Noriaki Matsunaga, Kazushige Nomura
    Physical Review B 97 (10) 104404  2469-9969 2018/03/05 [Refereed][Not invited]
     
    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.
  • Paramita Kar, Masaki Yoshida, Yasuhiro Shigeta, Akane Usui, Atsushi Kobayashi, Takaaki Minamidate, Noriaki Matsunaga, Masako Kato
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 56 (9) 2345 - 2349 1433-7851 2017/02 [Refereed][Not invited]
     
    A highly methanol-selective vapochromic response has been realized in a Ni-II-quinonoid complex, [Ni(HLMe)(2)] (H2LMe=4-methylamino-6-methyliminio-3-oxocyclohexa-1,4-dien-1-olate) which exhibits a reversible structural transformation including a coordination geometrical change between the square-planar and octahedral structure by the selective uptake of methanol vapor. This was accompanied by a remarkable color change between purple and orange, as well as temperature-robust spin-state switching in the solid state under ambient conditions. It is remarkable that the properties are derived by the fine structural modification of the quinonoid ligand such as methyl or ethyl analogues. Such a system has high potential for applications in memory devices as well as chemical sensors and smart responsive materials.
  • Paramita Kar, Masaki Yoshida, Yasuhiro Shigeta, Akane Usui, Atsushi Kobayashi, Takaaki Minamidate, Noriaki Matsunaga, Masako Kato
    Angewandte Chemie Wiley 129 (9) 2556  2017/02 [Refereed][Not invited]
  • Paramita Kar, Masaki Yoshida, Yasuhiro Shigeta, Akane Usui, Atsushi Kobayashi, Takaaki Minamidate, Noriaki Matsunaga, Masako Kato
    Angewandte Chemie Wiley 129 (9) 2385  2017/02 [Refereed][Not invited]
  • Paramita Kar, Masaki Yoshida, Yasuhiro Shigeta, Akane Usui, Atsushi Kobayashi, Takaaki Minamidate, Noriaki Matsunaga, Masako Kato
    Angewandte Chemie International Edition Wiley 56 (9) 2514  2017/02 [Refereed][Not invited]
  • T. Minamidate, N. Matsunaga, K. Nomura, T. Sasaki
    EPL 115 (3) 0295-5075 2016/08 [Refereed][Not invited]
     
    Magnetoresistance and Hall resistance measurements were conducted in the field-induced spin-density-wave (FISDW) phase of (TMTSF)(2)ReO4 above 1.0GPa, with an anion ordering specified by Q(AO) = (0, 1/2, 1/2). The quantized Hall resistance shows the sequence N = 0, 1, 2,-2, 4,-4,-6,-8, ... , with decreasing field that is successfully explained by the "extended standard model". Consequently, we demonstrate that the difference between the chemical and hydrostatic pressures is linked to the appearance of the peculiar FISDW phase of the TMTSF salts with Q(AO) = (0, 1/2, *). Copyright (C) EPLA, 2016
  • Yuki Oka, Noriaki Matsunaga, Kazushige Nomura, Atsuhi Kawamoto, Kaoru Yamamoto, Kyuya Yakushi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 (11) 0031-9015 2015/11 [Refereed][Not invited]
     
    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.
  • Takaaki Minamidate, Yuki Oka, Hironori Shindo, Toshitaka Yamazaki, Noriaki Matsunaga, Kazushige Nomura, Atsushi Kawamoto
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 (6) 0031-9015 2015/06 [Refereed][Not invited]
     
    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.
  • Yuki Oka, Hiroyoshi Nobukane, Noriaki Matsunaga, Kazushige Nomura, Kazuhiro Katono, Koichi Ichimura, Atsushi Kawamoto
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 (6) 0031-9015 2015/06 [Refereed][Not invited]
     
    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.
  • Y. Oka, H. Nobukane, N. Matsunaga, K. Nomura, K. Katono, K. Ichimura, A. Kawamoto
    PHYSICA B-CONDENSED MATTER 460 93 - 95 0921-4526 2015/03 [Refereed][Not invited]
     
    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.
  • 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 0921-4526 2015/03 [Refereed][Not invited]
     
    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
  • Noriaki Matsunaga, Shinji Hirose, Naoki Shimohara, Takehito Satoh, Tomoyuki Isome, Masatoshi Yamomoto, Yang Liu, Atsushi Kawamoto, Kazushige Nomura
    PHYSICAL REVIEW B 87 (14) 144415  1098-0121 2013/04 [Refereed][Not invited]
     
    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
  • Miko Matsumoto, Hiroki Kato, Yuki Kuwata, Atsushi Kawamoto, Noriaki Matsunaga, Kazushige Nomura
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 (11) 114709  0031-9015 2012/11 [Refereed][Not invited]
     
    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.
  • 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 022090  1742-6588 2012 [Refereed][Not invited]
     
    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.
  • Noriaki Matsunaga, Tomonori Akita, Koichi Ichimura, Kazushige Nomura, Atsushi Kawamoto
    PHYSICA B-CONDENSED MATTER 405 (11) S108 - S110 0921-4526 2010/06 [Refereed][Not invited]
     
    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
  • K. Nomura, N. Shimohara, D. Denda, N. Matsunaga, A. Kawamoto
    PHYSICA B-CONDENSED MATTER 405 (11) S116 - S119 0921-4526 2010/06 [Refereed][Not invited]
     
    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
  • Shinji Hirose, Atsushi Kawamoto, Noriaki Matsunaga, Kazushige Nomura, Kaoru Yamamoto, Kyuya Yakushi
    PHYSICAL REVIEW B 81 (20) 205107  1098-0121 2010/05 [Refereed][Not invited]
     
    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).
  • Yoshihiro Eto, Atsushi Kawamoto, Noriaki Matsunaga, Kazushige Nomura, Kaoru Yamamoto, Kyuya Yakushi
    PHYSICAL REVIEW B 80 (17) 174506  1098-0121 2009/11 [Refereed][Not invited]
     
    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.
  • Eto Yoshihiro, Kawamoto Atsushi, Matsunaga Noriaki, Nomura Kazushige, Yamamoto Kaoru, Yakushi Kyuya
    PHYSICAL REVIEW B 80 (17) 2469-9950 2009/11 [Refereed][Not invited]
  • K. Nomura, R. Muraoka, N. Matsunaga, K. Ichimura, J. Yamada
    PHYSICA B-CONDENSED MATTER 404 (3-4) 562 - 564 0921-4526 2009/03 [Refereed][Not invited]
     
    We have investigated the gap symmetry in the superconducting phase of beta-(BDA-TTP)(2)SbF6 with use of the scanning tunneling microscope (STM). The tunneling spectra obtained on the conducting surface show a clear superconducting gap structure. its functional form is of V-shaped similarly to kappa-(BEDT-TTF)(2)X and suggests the anisotropic superconducting gap with line nodes. For lateral surfaces the shape of tunneling spectra varies from the U-shape with relatively large gap to the V-shape with small gap depending on the tunneling direction alternately twice between directional angle 0 and pi. From the analysis of conductance curve taking the k dependence of the tunneling probability into account, it is found that the gap has maximum near the a* and c* axes and the nodes appear along near a* + c* and the a-c* directions. These indicate that the d(x)(-y)(2)(2) like superconducting pair is formed in this system as the case of kappa-(BEDT-TTF)(2)X. This node direction is consistent with the theoretical prediction based on the spin fluctuation mechanism. However, the zero-bias conductance peak has not been observed yet. (C) 2008 Elsevier B.V. All rights reserved.
  • Noriaki Matsunaga, Takehito Satoh, Koichi Ichimura, Kazushige Nomura, Atsushi Kawamoto
    PHYSICA B-CONDENSED MATTER 404 (3-4) 389 - 391 0921-4526 2009/03 [Refereed][Not invited]
     
    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.
  • Atsushi Kawamoto, Yosuke Honma, Ken-ichi Kumagai
    PHYSICAL REVIEW B 74 (21) 212508  1098-0121 2006/12 [Refereed][Not invited]
     
    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.
  • Noriaki Matsunaga, Katutosi Hino, Takamichi Ohta, Katsumi Yamashita, Kazushige Nomura, Takahiko Sasaki, Maki Watanabe, Jun-ichi Yamada, Shin'ichi Nakatsuji
    JOURNAL OF LOW TEMPERATURE PHYSICS 142 (3-4) 473 - 476 0022-2291 2006/02 [Refereed][Not invited]
     
    Hall resistance and magnetic torque measurements have been carried out in the field-induced spin-density-wave (FISDW) phase of deuterated (TMTSF)(2)ClO(4) for various cooling rates through the anion ordering temperature. We have found that the Hall resistance in the intermediate cooled state shows a phase transition from the non-quantized Hall phase to the quantized Hall phase (n=1) with hysteresis. We have also found that the magnetic torque in the non-quantized Hall phase rapidly decreases with increasing cooling rate. These results suggest that there is a new phase transition from the non-quantized Hall phase to the quantized Hall phase in (TMTSF)(2)ClO(4).
  • Noriaki Matsunaga, Katutosi Hino, Takamichi Ohta, Katsumi Yamashita, Kazushige Nomura, Takahiko Sasaki, Maki Watanabe, Jun-ichi Yamada, Shin'ichi Nakatsuji
    JOURNAL OF LOW TEMPERATURE PHYSICS 142 (3-4) 473 - 476 0022-2291 2006/02 [Refereed][Not invited]
     
    Hall resistance and magnetic torque measurements have been carried out in the field-induced spin-density-wave (FISDW) phase of deuterated (TMTSF)(2)ClO(4) for various cooling rates through the anion ordering temperature. We have found that the Hall resistance in the intermediate cooled state shows a phase transition from the non-quantized Hall phase to the quantized Hall phase (n=1) with hysteresis. We have also found that the magnetic torque in the non-quantized Hall phase rapidly decreases with increasing cooling rate. These results suggest that there is a new phase transition from the non-quantized Hall phase to the quantized Hall phase in (TMTSF)(2)ClO(4).
  • K Nomura, K Ishimura, K Fujimoto, N Matsunaga, T Nakamura, T Takahashi, G Saito
    JOURNAL DE PHYSIQUE IV 131 111 - 114 1155-4339 2005/12 [Refereed][Not invited]
     
    We have investigated the sliding motion of the SDW in the organic compound (TMTTF)(2)Br under the pressure with the measurement of the non-linear conductivity. Below the SDW transition temperature T-SDW, we observed the sharp increase of conductivity with the clear threshold electric field E-T, associated with the depinning of the SDW. For the typical sample, the temperature dependence of E-T shows a peak around 0.3(SDW) in each pressure. In addition, the field hysteresis with the switching appears in the dc I-V characteristics around 03T(SDW). The excess conductivity, dominated by the kinetic friction, shows a sharp increase below 0.3T(SDW). These behaviors indicate that the sliding mechanism of SDW varies across 0.3(SDW), which is almost equal to the sub-phase transition temperature. This fact suggests that the transition at 0.37(SDW) is associated with both the magnetic and charge degrees of freedom.
  • N Matsunaga, K Hino, T Ohta, K Yamashita, K Nomura, T Sasaki, A Ayari, P Monceau, M Watanabe, J Yamada, S Nakatsuji
    JOURNAL DE PHYSIQUE IV 131 269 - 272 1155-4339 2005/12 [Refereed][Not invited]
     
    We have measured Hall resistance and magnetic torque in the field-induced spin-density-wave (FISDW) phase of deuterated (TMTSF)(2)CLO4 for various cooling rates through the anion ordering temperature. The Hall resistance with the magnetic field parallel to c* is not sensitive to cooling rate above 16T. On the other hand, the Hall resistance between 9 and 14 T rapidly and continuously decreases with increasing cooling rate. This result means that the Flail resistance in the semimetallic SDW phase between 9 and 14 T is not quantized in the intermediate cooled states. A new phase transition from the non-quantized phase to the quantized (n = 1) Hall phase exists with hysteresis of the Hall resistance. Moreover, the new phase boundary is shifted towards a lower field when the cooling rate is increased. We have also found that the magnetic torque in the non-quantized phase rapidly decreases with increasing cooling rate. A possible ground state of non-quantized and Hall phase of the FISDW phase of (TMTSF)(2)CLO4 is discussed from the viewpoint of the peculiar SDW nesting vector.
  • K Nomura, K Ishimura, N Matsunaga, T Nakamura, T Takahashi, G Saito
    SYNTHETIC METALS 153 (1-3) 433 - 436 0379-6779 2005/09 [Refereed][Not invited]
     
    The spin-density wave (SDW) phase with an incommensurate wave vector is induced as a ground state in the organic compound (TMTTF)(2)Br under the pressure above 0.5 GPa. We investigated the collective sliding motion of the SDW condensate with measuring the non-linear conductivity in this SDW phase. The measurement was done with dc and pulse methods. Below the SDW transition temperature T-SDW, the sharp increase of conductivity from the ohmic one was observed with the clearly defined threshold electric field E-T. This indicates the depinning of the SDW and the excess conductivity above E-T is associated with the sliding motion of the SDW. The absolute value of E-T is fairly larger than that observed in (TMTSF)(2)PF6, whose ground state is the incommensurate SDW at ambient pressure. With decreasing the temperature from T-SDW, E-T increases gradually and shows a relatively sharp drop after a peak around 0.3T(SDW). This temperature is supposed to be connected with the sub-phase transition proposed from the temperature dependence of NMR relaxation rate. In addition, the excess conductivity normalized to the ohmic one, which corresponds to the current carried by the SDW condensate, shows a dip at 0.3T(SDW) with decreasing the temperature. In the dc I-V characteristics, the hysteretic behavior near E-T appears only around 0.3T(SDW). These behaviors suggest that the sliding mechanism of the SDW condensate varies across 0.3T(SDW). We discuss the dynamics of the SDW in (TMTTF)(2)Br in comparison with that in (TMTSF)(2)X, considering the sub-phase transition.
  • A Ishikawa, N Matsunaga, K Nomura, T Sasaki, T Nakamura, T Takahashi, G Saito
    PHYSICAL REVIEW B 67 (21) 1098-0121 2003/06 [Refereed][Not invited]
     
    The incommensurate spin-density-wave (SDW) phase in (TMTTF)(2)Br was investigated through transport measurements under pressure and magnetic fields parallel to the c(*) axis. For the incommensurate SDW phase of (TMTTF)(2)Br stabilized above 0.5 GPa, the SDW transition temperature T-SDW increases with the applied magnetic field. The field dependence of T-SDW is described by a quadratic behavior and the coefficient of the quadratic term increases with increasing pressure. These results are consistent with the prediction of the mean-field theory based on the suppression of the SDW transition by two dimensionality. From the relation between the coefficient of the quadratic term and T-SDW at zero magnetic field, we determined the role of electron correlation and two dimensionality in the SDW phase of (TMTTF)(2)Br under pressure and found that the SDW transition in (TMTTF)(2)Br can be well explained within the mean-field theory by taking into account the reduction of the coupling constant N(0)I by pressure.
  • K Nomura, T Terazaki, A Hoshikawa, N Matsunaga, M Watanabe, S Nakatsuji, J Yamada
    PHYSICA B-CONDENSED MATTER 329 1193 - 1194 0921-4526 2003/05 [Not refereed][Not invited]
     
    In the SDW phase of (TMTSF-d(12))(2)ClO4 induced by the rapid cooling, the non-linear electric conductivity with a threshold field E-T was observed, associated with the sliding motion of SDW. The monotonous increase of E-T against the temperature is explained with the strong pinning. The sharp drop of excess conductivity below 0.3T(SDW) and the temperature independent I-V characteristic suggest the quantum origin for the SDW sliding. (C) 2003 Elsevier Science B.V. All rights reserved.
  • N Matsunaga, K Yamashita, T Oota, K Nomura, T Sasaki, T Hanajiri, J Yamada, S Nakatsuji
    PHYSICA B-CONDENSED MATTER 329 1154 - 1155 0921-4526 2003/05 [Refereed][Not invited]
     
    Magnetoresistance measurements have been carried out along the highly conducting a-axis in the field-induced SDW (FISDW) phase of (TMTSF)(2)PF6 under 1.0 GPa, with the field up to 27 T parallel to the lowest-conductivity direction c*. We have determined the phase boundary between the last semimetallic FISDW phase with n = 1 and the FISDW insulating phase with n = 0 and found that the semimetallic FISDW phase existed above the transition temperature of the FISDW insulating phase at least up to 24 T. These results suggest the necessity of the theoretical calculation for more realistic quasi-one-dimensional Fermi surface to explain the FISDW phase of (TMTSF)2PF6. (C) 2003 Elsevier Science B.V. All rights reserved.
  • N. Matsunaga, K. Yamashita, M. Yamashita, A. Kawamoto, K. Nomura
    Physica C: Superconductivity and its Applications 388-389 591 - 592 0921-4534 2003/05/01 [Not refereed][Not invited]
     
    The phase diagram of κ-(BEDT-TTF)2Cu[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. © 2003 Elsevier Science B.V. All rights reserved.
  • N Matsunaga, K Yamashita, A Ayari, P Monceau, A Ishikawa, K Nomura, M Watanabe, J Yamada, S Nakatsuji
    SYNTHETIC METALS 135 (1-3) 621 - 622 0379-6779 2003/04 [Not refereed][Not invited]
     
    The transverse magnetoresistance of deuterated (TMTSF)(2)ClO4 for various cooling rates has been measured, with the field up to 28T parallel to the lowest conductivity direction c*. We describe the cooling rate dependence of rapid oscillations (RO) in the magnetoresistance inside the spin-density-wave (SDW) and the field-induced SDW (FISDW) state. We have found that two different RO in the semimetallic FISDW phase of relaxed (TMTSF)(2)ClO4 became undistinguishable, with increasing cooling rate.
  • A. Hoshikawa, T. Terazaki, N. Matsunaga, K. Nomura, M. Watanabe, S. Nakatsuji, J. Yamada
    Synthetic Metals 133-134 57 - 59 0379-6779 2003/03/13 [Not refereed][Not invited]
     
    We have investigated the electrical transport properties in both (TMTSF)2ClO4 and deuterated (TMTSF-d12)2ClO4. In (TMTSF-d12)2ClO4, we observed the anion ordering at TAO = 27 K with a resistance drop as well as (TMTSF)2ClO4, where TAO = 24 K. When the sample is quenched rapidly, the highest TSDW is obtained as 6 and 5 K in (TMTSF)2ClO4 and (TMTSF-d12)2ClO4, respectively. This difference indicates that the two-dimensionality of the electronic band in (TMTSF-d12)2ClO4 is stronger than that in (TMTSF)2ClO4. We also observed the non-linear electric conductivity with the threshold electric field ET associated with the sliding of spin-density-wave (SDW) in (TMTSF-d12)2ClO4. The value of ET sharply increases with decreasing temperature just below TSDW and becomes almost constant around 0.6TSDW. In addition, ET shows another increase below 0.4TSDW. In (TMTSF)2ClO4, ET is monotonically decreases with decreasing temperature and the temperature dependence becomes weaker as TSDW decreases. These behaviors are attributed to the difference of the mechanism of SDW sliding between two compounds. © 2002 Elsevier Science B.V. All rights reserved.
  • A. Ishikawa, N. Matsunaga, K. Nomura, T. Nakamura, T. Takahashi, G. Saito
    Synthetic Metals 133-134 65 - 66 0379-6779 2003/03/13 [Not refereed][Not invited]
     
    Resistivity measurements were performed on (TMTTF)2Br under pressure. Magnetic field was applied along c*-axis up to 16 T. Above 0.5 GPa, (TMTTF)2Br exhibits incommensurate spin density wave (ISDW) transition at low temperature. With increasing pressure, spin density wave (SDW) transition temperature TSDW decreases from 19.5 K at 0.5 GPa to 12.5 K at 2.1 GPa. In the incommensurate SDW phase, with increasing magnetic field, TSDW increases quadratically and the coefficient of quadratic term increases with increasing pressure. These results are qualitatively consistent with the prediction of the mean-field theory based on the imperfection of the nesting of Fermi surface. The relation between the coefficient of the quadratic term and TSDW at zero magnetic field can be explained by the mean-field theory with taking into account the reduction of the coupling constant N(0)I by pressure. © 2002 Elsevier Science B.V. All rights reserved.
  • N Matsunaga, A Ayari, P Monceau, A Ishikawa, K Nomura, M Watanabe, J Yamada, S Nakatsuji
    SYNTHETIC METALS 133 61 - 62 0379-6779 2003/03 [Not refereed][Not invited]
     
    Magnetoresistance measurements along the highly conducting a-axis have been carried out in deuterated (TMTSF-d(12))(2)ClO4 for various cooling rates through the anion ordering transition. Magnetic field up to 28 T was applied parallel to the c* direction. For a slow cooling, the field-induced spin-density-wave (FISDW) transition temperature, almost independent of field above 15 T in hydrogenated (TMTSF-h(12))(2)ClO4, slightly decreases with increasing field above 20 T in deuterated ones and the phase boundary at 27 T in hydrogenated samples appears at higher field in deuterated ones. The increase of the cooling rate shifts this phase boundary towards a lower field while the FISDW transition temperature increases with increasing field. The cooling rate dependence of the FISDW transition and the phase boundary at high magnetic fields in the (TMTSF-d(12))(2)ClO4 salts can be explained by the decrease of the dimerized gap due to anion ordering. (C) 2002 Elsevier Science B.V. All rights reserved.
  • K Yamashita, N Matsunaga, K Nomura, T Sasaki, T Hanajiri, J Yamada, S Nakatsuji, H Anzai
    SYNTHETIC METALS 133 63 - 64 0379-6779 2003/03 [Refereed][Not invited]
     
    The transverse magnetoresistance has been measured in (TMTSF)(2)PF6 under pressure, with the field parallel to the c* axis. At 0.85 GPa, the spin-density-wave (SDW) transition temperature T-SDW increases quadratically with the applied magnetic field, and a saturation behavior is observed in high magnetic fields. These results are consistent with the mean field theory. From these behaviors, T-SDW for the perfect nesting case, Fermi velocity and imperfect nesting parameter at 0.85 GPa are estimated as T-SDW0 = 14.5 K, nu(F) = 8.55 x 10(4) m/s and epsilon(0)/Delta(0) = 0.996 using the mean field theory, respectively. The SDW phase diagram of (TMTSF)(2)X can be described by taking into account the reduction of the coupling constant by the pressure. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Magnetic Field Dependence of the SDW Phase in (TMTSF)2PF6 under Pressure K. Yamashita, N. Matsunaga, K. Nomura, T. Sasaki, T. Hanajiri, J. Yamada, S. Nakatsuji, H. Anzai Synthetic Metals 133-134 P. 63-64 (2003)*
    2003 [Not refereed][Not invited]
  • Field-induced SDW phase diagram of (TMTSF)2PF6 at high magnetic fields N. Matsunaga, K. Yamashita, T. Oota, K. Nomura, T. Sasaki, T. Hanajiri, J. Yamada, S. Nakatsuji Physica B 329-333P2 pp. 1154-1155 (2003)*
    2003 [Not refereed][Not invited]
  • Phase diagram of partially deuterated k-(BEDT-TTF)2Cu[N(CN)2]Br N. Matsunaga, K. Yamashita, M. Yamashita, A. Kawamoto, K. Nomura Physica C 388-389C pp. 591-592 (2003)*
    2003 [Not refereed][Not invited]
  • Electron correlation and two-dimensionality in the spin-density-wave phase of (TMTTF)2Br under pressure A. Ishikawa, N. Matsunaga, K. Nomura, T. Sasaki, T. Nakamura, T. Takahashi, G. Saito Physical Review B Vol.67, 212404 (2003)*
    2003 [Not refereed][Not invited]
  • N Matsunaga, A Ayari, P Monceau, K Yamashita, A Ishikawa, K Nomura, M Watanabe, J Yamada, S Nakatsuji
    JOURNAL DE PHYSIQUE IV 12 (PR9) 381 - 384 1155-4339 2002/11 [Not refereed][Not invited]
     
    Magnetoresistance and Hall resistance measurements have been carried out in the FISDW phase of deuterated (TMTSF)(2)ClO4 for various cooling rates through the anion ordering temperature. The Hall resistance in the intermediate cooled state, observed a very stable quantum Hall state above 9.0 T for slowly cooled, shows a step-like change from the phase between 10 and 17 T to the phase between 20 and 25 T with hysteresis between 14 and 21 T. This result suggests that there is a new phase transition around 15 T in deuterated (TMTSF)(2)ClO4. A possible ground state of the FISDW phase of (TMTSF)(2)ClO4 for various cooling rates is discussed from the viewpoint of the peculiar SDW nesting vector stabilized by the dimerized gap due to anion ordering.
  • N Matsunaga, A Ayari, P Monceau, A Ishikawa, K Nomura, M Watanabe, J Yamada, S Nakatsuji
    PHYSICAL REVIEW B 66 (2) 1098-0121 2002/07 [Not refereed][Not invited]
     
    Magnetoresistance measurements have been carried out along the highly conducting a axis in the field-induced spin-density wave (FISDW) phase of hydrogenated and deuterated (TMTSF)(2)ClO4 for various cooling rates through the anion ordering temperature. With increasing the cooling rate, (i) the high-field phase boundary beta(HI), observed at 27 T in hydrogenated samples for slowly cooled, is shifted towards a lower field, (ii) the last semimetallic SDW phase below beta(HI) is suppressed, and (iii) the FISDW insulating phase above beta(HI) is enhanced in both salts. The cooling rate dependence of the FISDW transition and of beta(HI) in both salts can be explained by taking into account the peculiar SDW nesting vector stabilized by the dimerized gap due to anion ordering.
  • N Matsunaga, A Ayari, P Monceau, A Ishikawa, K Nomura, M Watanabe, J Yamada, S Nakatsuji
    PHYSICAL REVIEW B 66 (2) 1098-0121 2002/07 [Refereed][Not invited]
     
    Magnetoresistance measurements have been carried out along the highly conducting a axis in the field-induced spin-density wave (FISDW) phase of hydrogenated and deuterated (TMTSF)(2)ClO4 for various cooling rates through the anion ordering temperature. With increasing the cooling rate, (i) the high-field phase boundary beta(HI), observed at 27 T in hydrogenated samples for slowly cooled, is shifted towards a lower field, (ii) the last semimetallic SDW phase below beta(HI) is suppressed, and (iii) the FISDW insulating phase above beta(HI) is enhanced in both salts. The cooling rate dependence of the FISDW transition and of beta(HI) in both salts can be explained by taking into account the peculiar SDW nesting vector stabilized by the dimerized gap due to anion ordering.
  • N. Matsunaga, A. Ayari, P. Monceau, A. Ishikawa, K. Nomura, M. Watanabe, J. Yamada, S. Nakatsuji
    Physical Review B - Condensed Matter and Materials Physics 66 (2) 244251 - 244255 0163-1829 2002/07/01 [Refereed][Not invited]
     
    Magnetoresistance measurements have been carried out along the highly conducting a axis in the field-induced spin-density wave (FISDW) phase of hydrogenated and deuterated (TMTSF)2ClO4 for various cooling rates through the anion ordering temperature. With increasing the cooling rate, (i) the high-field phase boundary βHI, observed at 27 T in hydrogenated samples for slowly cooled, is shifted towards a lower field, (ii) the last semimetallic SDW phase below βHI is suppressed, and (iii) the FISDW insulating phase above βHI is enhanced in both salts. The cooling rate dependence of the FISDW transition and of βHI in both salts can be explained by taking into account the peculiar SDW nesting vector stabilized by the dimerized gap due to anion ordering.
  • Matsunaga N., Yamashita K., Kotani H., Nomura K.
    PHYSICAL REVIEW B, American Physical Society 64 (5) 52405 - 52405 0163-1829 2001/08/01 
    The transverse magnetoresistance of the Bechgaard salt (TMTSF)2PF6 has been measured for various pressures, with the field up to 24 T parallel to the lowest-conductivity direction c*. A quadratic behavior is observed in the magnetic-field dependence of the spin-density-wave (SDW) transition temperature TSDW. With increasing pressure, TSDW decreases and the coefficient of the quadratic term increases. These results are consistent with the prediction of the mean-field theory based on the nesting of the quasi-one-dimensional Fermi surface. Using a mean-field theory, TSDW for the perfect nesting case is estimated as about 16 K. This means that even at ambient pressure where TSDW is 12 K, the SDW phase of (TMTSF)2PF6 is substantially suppressed by the two dimensionality of the system.
  • A Ishikawa, N Matsunaga, K Nomura, T Nakamura, T Takahashi, G Saito
    SYNTHETIC METALS 120 (1-3) 905 - 906 0379-6779 2001/03 [Not refereed][Not invited]
     
    We investigated the pressure dependence of the resistivity in (TMTTF)(2)Br, applying with pressure up to 1.2GPa. At ambient pressure the resistance shows the kink structure at 18K where the spin susceptibility starts to decrease, despite the AF transition occurs at 14K. With increasing pressure, the peak of the derivative of the resistance appears 4-8K above the AF transition. It's suggested to be the new phase transition above the AF transition. Above 0.5GPa, the pressure dependence of T-SDW is consistent with the prediction of the mean field theory.
  • K Nomura, M Kotomizu, A Hoshikawa, T Terazaki, M Inoue, N Matsunaga
    SYNTHETIC METALS 120 (1-3) 907 - 908 0379-6779 2001/03 [Refereed][Not invited]
     
    The static and dynamic properties of incommensurate SDW phase in (TMTSF)(2)PF6 were investigated by the NMR and non-linear conductivity measurements. The temperature dependence of 1 indicates the sub-phase transition in the SDW phase. In the low temperature SDW sub-phase, the non-linear conductivity, associated with the sliding motion of the SDW, is observed with a clear threshold field. In addition, the temperature independent non-linear conductivity appears for a higher electric field and its field dependence suggests the quantum origin. These behaviours are discussed in the viewpoint of the SDW with the discommensuration.
  • SPIN DENSITY WAVE IN QUASI-ONE DIMENSIONAL ORGANIC CONDUCTORS K. Nomura, N. Matsunaga, A. Ishikawa, H. Kotani, K. Yamashita, T. Sasaki, T. Hanajiri, J. Yamada, S. Nakatsuji, H. Anzai, T. Nakamura, T. Takahashi and G. Saito physica status solidi (b) 223・・・
    2001 [Not refereed][Not invited]
     
    SPIN DENSITY WAVE IN QUASI-ONE DIMENSIONAL ORGANIC CONDUCTORS
    K. Nomura, N. Matsunaga, A. Ishikawa, H. Kotani, K. Yamashita, T. Sasaki, T. Hanajiri, J. Yamada, S. Nakatsuji, H. Anzai, T. Nakamura, T. Takahashi and G. Saito
    physica status solidi (b) 223 No.2 P.449-458 (2001)*
  • SDW phase of (TMTSF)2PF6 at high magnetic fields N. Matsunaga, H. Kotani, K. Yamashita, K. Nomura, T. Sasaki, T. Hanajiri, J. Yamada, S. Nakatsuji, H. Anzai Synthetic Metals 120 P.957-958 (2001)*
    2001 [Not refereed][Not invited]
  • A. Ishikawa, N. Matsunaga, K. Nomura, T. Nakamura, T. Takahashi, G. Saito
    Physica Status Solidi (B) Basic Research 223 (2) 539 - 543 0370-1972 2001/01 [Not refereed][Not invited]
     
    Resistivity and static magnetization measurements were performed in the organic compound (TMTTF)2Br. The resistivity was measured with applying pressure up to 2.1 GPa. At ambient pressure the resistance shows a kink at 18 K and the spin susceptibility starts to decrease at 19 K. The resistance shows no characteristic structure around TAF. With increasing pressure, the kink structure changes its shape to a peak in the derivative of the logarithm of the resistance with 1/T. The peak temperature increases with increasing pressure up to 0.3 GPa and is 4-8 K higher than TAF. This indicates the existence of another phase just above the AF state.
  • NON-LINEAR ELECTRIC CONDUCTION IN THE SDW PHASE OF (TMTSF)2PF6 UNDER PRESSURE N. Matsunaga, M. Inoue, A. Hoshikawa, K. Nomura, T. Hanajiri, J. Yamada, S. Nakatsuji, H. Anzai physica status solidi (b) 223 No.2 P.549-553 (2001)*
    2001 [Not refereed][Not invited]
  • N. Matsunaga, K. Yamashita, H. Kotani, K. Nomura, T. Sasaki, T. Hanajiri, J. Yamada, S. Nakatsuji, H. Anzai
    Physica Status Solidi (B) Basic Research 223 (2) 545 - 548 0370-1972 2001/01 [Not refereed][Not invited]
     
    The transverse magnetoresistance of the Bechgaard salt (TMTSF)2PF6, for various pressures has been measured, with the field up to 27 T parallel to the lowest conductivity direction c*. We describe the pressure dependence of a single series of rapid oscillations (RO) in the magnetoresistance inside the spin-density-wave (SDW) state. The oscillation frequency increases from 270 T at 0.21 GPa up to 310 T at 0.77GPa. A possible mechanism of the RO is discussed from the viewpoint of the commensurability between the SDW wavelength and the crystalline lattice.
  • Spin-density-wave transition of (TMTSF)2PF6 at high magnetic fields N. Matsunaga, K. Yamashita, H. Kotani, K. Nomura, T. Sasaki, T. Hanajiri, J. Yamada, S. Nakatsuji, H. Anzai Physical Review B Vol.64, 052405 (2001)*
    2001 [Not refereed][Not invited]
  • Static and Dynamic properties of the SDW in (TMTSF)2X K. Nomura, M. Kotomizu, A. Hoshikawa, T. Terazaki, M. Inoue, N. Matsunaga, T. Hanajiri, J. Yamada, S. Nakatsuji and H. Anzai Synthetic Metals 120 P.907-908 (2001)*
    2001 [Not refereed][Not invited]
  • N Matsunaga, M Inoue, A Hoshikawa, K Nomura, T Hanajiri, J Yamada, S Nakatsuji, H Anzai
    PHYSICA STATUS SOLIDI B-BASIC RESEARCH 223 (2) 549 - 553 0370-1972 2001/01 [Refereed][Not invited]
     
    We have measured the nonlinear conductivity with the threshold electric field Er in the spin-density-wave SDW) phase of (TMTSF)(2)PF6 under pressure to clarify the dynamics of SDW. The gradual temperature dependence of ET was observed under 0.21 GPa where T-SDW is 12.5 K and was explained in the classical strong pinning model. The normalized excess electric conductivity [sigma (2E(T)) - sigma (0)]/sigma (0) rapidly decreases below about T* similar or equal to 0.3T(SDW). In high electric fields Ear above ET, the temperature independent electric conduction expressed as the function j = j(0) exp (-E-0/E) is observed below T*. It is: suggested that the sliding of SDW with quantum origin occurs at low temperature. These phenomena are related to a phase transition dividing the SDW phase into two sub-phases in (TMTSF)(2)PF6. The electric conductivity in the low temperature sub-phase is discussed in terms of the SDW with discommensuration.
  • Matsunaga N, Kotani H, Yamashita K, Nomura K, Sasaki T, Hanajiri T, Yamada J, Nakatsuji S, Anzai H
    Synthetic Metals 120 (1-3) 957 - 958 0379-6779 2001 [Refereed][Not invited]
  • N Matsunaga, A Briggs, A Ishikawa, K Nomura, T Hanajiri, J Yamada, S Nakatsuji, H Anzai
    PHYSICAL REVIEW B 62 (13) 8611 - 8614 1098-0121 2000/10 [Not refereed][Not invited]
     
    The magnetic field dependence of the SDW transition in (TMTSF)(2)ClO4 for various anion cooling rates has been measured, with the field up to 27 T parallel to the lowest conductivity direction c*. For quenched (TMTSF)(2)ClO4, the SDW transition temperature T-SDW increases from 4.5 K in zero field up to 8.4 K at 27 T. A quadratic behavior is observed below 18 T, followed by a saturation behavior. These results are consistent with the prediction of the mean-field theory. From these behaviors, T-SDW is estimated as T-SDW0 = 13.5 K for the perfect nesting case. This indicates that the SDW phase in quenched (TMTSF)(2)ClO4, where T-SDW is less than 6 K, is strongly suppressed by the two-dimensionality of the system. In the intermediate cooled state in which the SDW phase does not appear in zero field, the transition temperature for the field-induced SDW shows a quadratic behavior above 12 T and there is no saturation behavior even at 27 T, in contrast to the FISDW phase in the relaxed state. This behavior can probably be attributed to the difference of the dimerized gap due to anion ordering.
  • N. Matsunaga, A. Briggs, A. Ishikawa, K. Nomura, T. Hanajiri, J. Yamada, S. Nakatsuji, H. Anzai
    Physical Review B - Condensed Matter and Materials Physics 62 (13) 8611 - 8614 0163-1829 2000/10/01 [Refereed][Not invited]
     
    The magnetic field dependence of the SDW transition in (TMTSF)2ClO4 for various anion cooling rates has been measured, with the field up to 27 T parallel to the lowest conductivity direction c*. For quenched (TMTSF)2ClO4, the SDW transition temperature TSDW increases from 4.5 K in zero field up to 8.4 K at 27 T. A quadratic behavior is observed below 18 T, followed by a saturation behavior. These results are consistent with the prediction of the mean-field theory. From these behaviors, TSDW is estimated as TSDW0 = 13.5 K for the perfect nesting case. This indicates that the SDW phase in quenched (TMTSF)2ClO4, where TSDW is less than 6 K, is strongly suppressed by the two-dimensionality of the system. In the intermediate cooled state in which the SDW phase does not appear in zero field, the transition temperature for the field-induced SDW shows a quadratic behavior above 12 T and there is no saturation behavior even at 27 T, in contrast to the FISDW phase in the relaxed state. This behavior can probably be attributed to the difference of the dimerized gap due to anion ordering.
  • N Matsunaga, A Briggs, A Ishikawa, K Nomura, S Takasaki, J Yamada, S Nakatsuji, H Anzai
    PHYSICA B 284 1581 - 1582 0921-4526 2000/07 [Not refereed][Not invited]
     
    The magnetic field dependence of the SDW transition (T-SDW) in quenched (TMTSF)(2)ClO4 has been measured up to 27 T, with the field parallel to the c*-direction. T-SDW increases from 4.5 K in zero held up to 8.4 K at 27 T. The field dependence of T-SDW has been calculated in the framework of the mean-field theory. As predicted, a quadratic behavior is observed at low field, followed by a saturation behavior. T-SDW corresponding to the perfect nesting case is estimated to be 13.5 K. This means that the SDW phase of quenched (TMTSF)(2) ClO4 is strongly suppressed by the two dimensionality of the system. (C) 2000 Elsevier Science B.V. All rights reserved.
  • N Matsunaga, K Nomura, T Nakamura, T Takahashi, G Saito, S Takasaki, J Yamada, S Nakatsuji, H Anzai
    PHYSICA B 284 1583 - 1584 0921-4526 2000/07 [Not refereed][Not invited]
     
    We report on the static magnetic susceptibility in the spin density wave (SDW) phase of (TMTTF)(2)Br and (TMTSF)(2)AsF6. A decrease of the differential susceptibility of (TMTSF)(2)AsF6 was observed around 4 K. This anomaly indicates a difference of the spin canting above and below the critical temperature. In the measurements of magnetic susceptibility on the commensurate SDW phase of (TMTTF), Br, a large decrease of the spin susceptibility was observed above T-SDW and non-activated-type behavior in the b'-axis susceptibility was observed below the spin-flop field at low temperature. The data are discussed on the basis of commensurability. (C) 2000 Elsevier Science B.V. All rights reserved.
  • N Matsunaga, A Briggs, A Ishikawa, K Nomura, S Takasaki, J Yamada, S Nakatsuji, H Anzai
    JOURNAL DE PHYSIQUE IV 9 (P10) 211 - 212 1155-4339 1999/12 [Not refereed][Not invited]
     
    The magnetic field dependence of the SDW transition in (TMTSF)(2)ClO4 for various anion quenching rates has been measured up to 27T, with the field parallel to the lowest conductivity direction c*. The SDW transition temperature T-SDW decreases with decreasing quenching rate and the rate of increase with magnetic field increases with decreasing T-SDW. For quenched (TMTSF)(2)ClO4, T-SDW increases from 4.5K in zero field up to 8.4K at 27T. As predicted, a quadratic behavior is observed below 18T, followed by a saturation behavior. These results are consistent with the prediction of the mean-field theory. For the perfect nesting case, T-SDW is estimated as T-SDW0 = 13.5K. This means that the SDW phase of quenched (TMTSF)(2)ClO4 is strongly suppressed by the two-dimensionality of the system. In the intermediate cooling state in which there is no SDW phase in zero field, T-SDW shows a quadratic behavior above 12T and there is no saturation even at 27T, which is different to the field induced SDW phase of the relaxed state. This may be attributed to the difference of the anion gap structure.
  • N Matsunaga, A Briggs, A Ishikawa, K Nomura, S Takasaki, J Yamada, S Nakatsuji, H Anzai
    JOURNAL DE PHYSIQUE IV 9 (P10) 211 - 212 1155-4339 1999/12 [Not refereed][Not invited]
     
    The magnetic field dependence of the SDW transition in (TMTSF)(2)ClO4 for various anion quenching rates has been measured up to 27T, with the field parallel to the lowest conductivity direction c*. The SDW transition temperature T-SDW decreases with decreasing quenching rate and the rate of increase with magnetic field increases with decreasing T-SDW. For quenched (TMTSF)(2)ClO4, T-SDW increases from 4.5K in zero field up to 8.4K at 27T. As predicted, a quadratic behavior is observed below 18T, followed by a saturation behavior. These results are consistent with the prediction of the mean-field theory. For the perfect nesting case, T-SDW is estimated as T-SDW0 = 13.5K. This means that the SDW phase of quenched (TMTSF)(2)ClO4 is strongly suppressed by the two-dimensionality of the system. In the intermediate cooling state in which there is no SDW phase in zero field, T-SDW shows a quadratic behavior above 12T and there is no saturation even at 27T, which is different to the field induced SDW phase of the relaxed state. This may be attributed to the difference of the anion gap structure.
  • N Matsunaga, Y Hosokawa, H Iwasaki, K Nomura, S Takasaki, J Yamada, S Nakatsuji, H Anzai, T Nakamura, T Takahashi, G Saito
    JOURNAL DE PHYSIQUE IV 9 (P10) 243 - 246 1155-4339 1999/12 [Refereed][Not invited]
     
    Magnetic properties of the spin density wave (SDW) phase in (TMTSF)(2)X (X=AsF6, PF6) and (TMTTF)(2)Br were investigated through. analyses of H-1-NMR and static magnetization measurements. A divergent peak was observed, at the temperature TC well below the SDW transition temperature, in the H-1 spin-lattice relaxation rate in the incommensurate SDW phase of (TMTSF)(2)X. A decrease of the differential magnetic susceptibility of (TMTSF)(2)X with the field parallel to the a-axis was observed around T*. This anomaly indicates a difference of the spin canting above and below T* which divides the SDW phase. In the measurements of magnetic susceptibility on the commensurate SDW phase of (TMTTF)2Br, a large decrease of the spin susceptibility was observed above T-SDW and non-activated type behavior in the b'-axis susceptibility is observed below the spin-flop field at low temperature. The data are discussed on the basis of commensurability.
  • N Matsunaga, N Gomi, K Nomura, H Tsuchiya, S Takasaki, J Yamada, S Nakatsuji, H Anzai
    SYNTHETIC METALS 103 (1-3) 2132 - 2132 0379-6779 1999/06 [Refereed][Not invited]
     
    We report on the static susceptibility in the SDW phase of (TMTSF)(2)AsF6 with field parallel to the a-axis. Anomalous susceptibility was observed around 4K. In this field direction, the susceptibility is given by the canting of anti-ferromagnetically ordering spins. This anomaly indicates the difference of the spin canting between above and below the critical temperature which divide the SDW phase.
  • N Matsunaga, A Ishikawa, K Nomura, S Takasaki, J Yamada, S Nakatsuji, H Anzai
    SYNTHETIC METALS 103 (1-3) 2133 - 2134 0379-6779 1999/06 [Refereed][Not invited]
     
    We have used electrical transport measurements to investigate the temperature and magnetic field dependence of the SDW transition in (TMTSF)(2)ClO4 for various anion quenching rates. The transition temperature decrease with decreasing quenching rate and the field dependence is nearly quadratic for fields in the c* direction. Even in the rapidly quenched phase, the transition temperature shows large increase by the field of 12T. This means that the SDW phase of quenched (TMTSF)(2)ClO4 is strongly suppressed by two-dimensionality of the system.
  • N.Matsunaga, A.Ishikawa, A.Hoshikawa, K.Nomura, S.Takasaki, J.Yamada, S.Nakatsuji, H.Anzai "Anion disorder and two-dimensionality in the superconducting and SDW states of (TMTSF)2ClO4" Journal of Low Temperature Physics 177 1735-1739 (1999)*
    1999 [Not refereed][Not invited]
  • N.Matsunaga, Y.Hosokawa, H.Iwasaki, K.Nomura, S.Takasaki, J.Yamada, S.Nakatsuji, H.Anzai, T.Nakamura, T.Takahashi, G.Saito "Magnetic properties of the spin-density wave in (TMTSF)2X and (TMTTF)2Br" J. Phys. IV France 9 Pr10-234-246(1999)*
    1999 [Not refereed][Not invited]
  • N. Matsunaga, N. Gomi, K. Nomura, H. Tsuchiya, S. Takasaki, J. Yamada, S. Nakatsuji and H. Anzai "STATIC MAGNETIC SUSCEPTIBILITY IN THE SDW PHASE OF (TMTSF)2X" Synthetic Metals 103, 2132(1999)*
    1999 [Not refereed][Not invited]
  • N Matsunaga, Y Okajima, K Nomura, S Takasaki, J Yamada, S Nakatsuji, H Anzai
    SYNTHETIC METALS 86 (1-3) 2119 - 2120 0379-6779 1997/02 [Refereed][Not invited]
     
    The transverse magnetoresistance (Delta rho/rho) of (TMTSF)(2)ClO4 has been measured at ambient pressure in the temperature range front 0.5K to 4.2K for various cooling rates through the ClO4- anion ordering temperature (similar to 24K). The transverse magnetoresistance is highly anisotropic for the field orientations in the plane perpendicular to the highly conducting a-axis. Por temperatures below the metal-SDW transition in the quenched state, the magnetoresistance has maximum when the magnetic field is parallel to the lowest conductivity direction c* and its value is temperature independent. In the metallic (relaxed) phase, magnetoresistance maximum occurs for a field direction b' in the field of 1.2T. With decreasing temperature, the value of b'-axis magnetoresistance continuously increases in the metallic phase.
  • Matsunaga, N., Okajima, Y., Nomura, K., Takasaki, S., Yamada, J., Nakatsuji, S. and Anzai, H. : "Anisotropic Magnetoresistance of (TMTSF)2ClO4 in the metallic and SDW state", Synthetic Metals, 86 : 2119-2120 (1997)＊
    1997 [Not refereed][Not invited]
  • N. Matsunaga, A. Hoshikawa, K. Nomura, T. Sambongi, M. Tokumoto, N. Kinoshita and H. Anzai : "Influence of the anion disorder in the superconducting phase of (TMTSF)２ClO４", Czech Jounal of Physica, 46(S2) : 807-808 (1996)＊
    1996 [Not refereed][Not invited]
  • N Matsunaga, A Hoshikawa, K Nomura, T Sambongi, M Tokumoto, N Kinosita, N Anzai
    CZECHOSLOVAK JOURNAL OF PHYSICS 46 807 - 808 0011-4626 1996 [Refereed][Not invited]
     
    The anion-disorder effect for the superconducting phase of (TMTSF)(2)ClO4 was investigated by resistance measurements for various cooling rates through the ClO4- anion ordering temperature. The resistivity along the a-axis monotonically decreases as decreasing temperature below the cooling rate of 0.3K/sec and the residual resistance caused by imperfectness of anion ordering increases as increasing cooling rate. The rate of T-C decrease is proportional to the one of nonmagnetic scattering decided from the residual resistivity, that is, dT(C)/d rho(a) similar to -1x10(5) (K/(Omega m)), where rho(a) is the resistivity along the a-axis at 1.5K.
  • N MATSUNAGA, H TAKESHIGE, R OKAJIMA, A HOSHIKAWA, K NOMURA, T SAMBONGI, M TOKUMOTO, N KINOSITA, H ANZAI
    SYNTHETIC METALS 70 (1-3) 763 - 764 0379-6779 1995/03 [Refereed][Not invited]
     
    The anion-ordering effect for the superconducting phase of (TMTSF)(2)ClO4 was investigated by both measurements of static magnetization and resistance for various coding rate through the ClO4- anion ordering temperature (similar to 24K). With increasing cooling rate, the temperature of superconducting transition, T-c, determined through the measurements of Meissner effect continuously decreases. The resistance along the a-axis monotonically decreases as decreasing temperature below the coding rate of 0.2K/sec and the residual resistance caused by imperfectness of anion ordering increases as increasing coding rate. The decrease of T-c is attributed to the pair breaking effect of nonmagnetic scattering due to the suppression of anion ordering.
  • K NOMURA, Y HOSOKAWA, N MATSUNAGA, M NAGASAWA, T SAMBONGI, H ANZAI
    SYNTHETIC METALS 70 (1-3) 1295 - 1296 0379-6779 1995/03 [Refereed][Not invited]
     
    The spin lattice relaxation rate T-1(-1) of H-1 was measured in the spin-density wave (SDW) phase of (TMTSF)(2)AsF6 and (TMTSF)(2)ClO4. In addition to the sharp peak observed at the SDW transition temperature T-SDW, the temperature dependence of T-1(-1) shows an another divergent peak at the temperature T* much lower than T-SDW in both materials. It was found that the observed value for T* is proportional to T-SDW with the slope T-SDW/T*=3.5. This behavior indicates that the mechanism of the divergent peak in T-1(-1) at T* is common in the SDW phase of (TMTSF)(2)X family and is closely related to the SDW transition. It is suggested that the structural change occurs in the SDW condensate.
  • K NOMURA, K NAGAO, K ICHIMURA, N MATSUNAGA
    SYNTHETIC METALS 70 (1-3) 911 - 912 0379-6779 1995/03 [Refereed][Not invited]
     
    The superconducting phase of (BEDT-TTF)(2)Cu(NCS)(2) was investigated with use of the scanning tunneling microscope (STM). The tunneling conductance was measured at the b-c surface of a single crystal. The differential conductance shows a clear superconducting gap structure below the transition temperature and its value is reduced to almost zero around zero bias voltage at 1.9 K. The conductance curve is not well fitted to the BCS one but suggests the gap anisotropy. However, the gap with line nodes, expected from the simple d-wave symmetry, is excluded. Possible models for the superconducting gap are as follows; (1) the gap with point nodes or (2) the anisotropic gap with a minimum value Delta(min) similar to 1 mev. It is understood that the superconducting gap is highly anisotropic in k-space.
  • N MATSUNAGA, H TAKESHIGE, T KEITOKU, M NAGASAWA, K NOMURA, T SAMBONGI
    PHYSICA B 194 1265 - 1266 0921-4526 1994/02 [Refereed][Not invited]
     
    We report on magnetic properties in the spin density wave (SDW) phase of (TMTSF)2X through analyses of H-1-NMR and static magnetization measurements. We observed a large enhancement of the spin-lattice relaxation rate of H-1 below the SDW transition temperature (T(SDW)). The temperature of this peak is proportional to the T(SDW). The measurements of magnetization also support this result. These are attributed to the new phase transition within the SDW state.

MISC

Books etc

Association Memberships

  • 日本物理学会   

Research Projects

  • 基盤研究(C)
    Date (from‐to) : 2019/04 -2022/03 
    Author : 松永 悟明
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2006 -2007 
    Author : 野村 一成, 市村 晃一, 松永 悟明
     
    ドナー分子の中心にTCF骨格を持たないβ-(BDA-TTP)_2SbF6_(T_c=7.5K)の超伝導相においてSTMを用いたトンネル分光測定を行った。この系は近隣め物質の振る舞いからκ-(BEDT-TTF)_2X系と同様に電子相関が強い2次元電子系と考えられるが、β-型の構造を持つためκ-(BEDT-TTF>_2Xのようなモット絶縁体に隣接した超伝導ではないと考えられ、そのルカニズムに興味が持たれる。 伝導面でのトンネルスペクトルはT_cよりも十分低温では、ゼロバイアス付近のコンダクタンスがほとんどゼロにまで減少する明確な超伝導ギャップ構造を示す。その関数系はκ-(BEDT-TTF)_2X系と同様にV-型を示しており、ラインノードを持った異方的超伝導であることを示している。一方、側面でのトンネルスペクトルは、面の角度に応じて比較的大きなギャップを持ったU-型から小さなギャップのV-型に角度πの間に2回変化することが明らかになった。トンネル遷移確率の方向依存性を考慮し軸近辺でギャップ最大となり、軸近辺でギャップ最大となり、a^*+c^* a^*-c^*方向近辺でノードを持つことが強く示唆される。上述の結晶系のため、純粋なd(x^2-y^2)波対称性ではな いかもしれないがd(x^2-y^2)波的対称性が実現していると結論される。このノードの方向はフェルミ面の部分ネスティングによるスピン揺らぎから期待されるノード方向となっている。一方で、β-型における最近接分子間の超伝導電子対とはなっておらず、スピン揺らぎによる超伝導のメカニズムを支持しているように思われる。しかし、ノードを伴う異方的超伝導の証拠とされるZBCPは現在までに観測されておらず、今後の課題である。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2005 -2006 
    Author : ICHIMURA Koichi, MATSUNAGA Noriaki
     
    Layered compound NbSe_2 nanotubes were studied by low temperature scanning tunneling microscope (STM). NbSe_2 nanotube is an interesting material since it is the first nanotube material, of which bulk phase undergoes the condensed state such as the density wave and superconductivity. NbSe_2 nanotubes were synthesized by the chemical vapor transport method. The nanotube sample for STM measurement was prepared by dropping NbSe_2 nanotubes agitated ultrasonically in 2-propanol on cleaved highly oriented pyrolytic graphite (HOPG). Topographic STM images of NbSe_2 nanotubes on the substrate of HOPG were taken at room temperature. The length of nanotubes is estimated as 300-2000 nm. Almost NbSe_2 nanotube has length over 600 nm. The nanotube structure is confirmed by STM scan profiles. Diameter of nanotubes is estimated as 2-50 nm, which is much smaller than that of multi-walled nanotubes studied by transmission electron microscope. We think that nanotubes with diameter of less than 10 nm are single-walled one. We are interested in the relation between the chirality (helicity) and electronic structure in single-walled NbSe_2 nanotubes. The bundle structure, which is popular in single-walled carbon nanotube, is found in NbSe_2 nanotubes. The bundle consists of about hundred nanotubes. The Y-junction, which is the connected structure with three nanotubes, is also found similarly to carbon nanotubes. Although we can not take STM image with atomic resolution at room temperature, clear images with atomic arrangement are obtained below 4.2 K. The chirality of NbSe_2 nanotube is successfully determined from these images. The chiral index is found to vary from sample to sample. We also find that all nanotubes, of which atomic arrangement is determined, are so-called chiral type with low symmetry in helicity. It might give some suggestion to growing mechanism of NbSe_2 nanotubes.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2004 -2005 
    Author : 野村 一成, 市村 晃一, 松永 悟明
     
    圧力下で誘起される擬一次元有機導体(TMTTF)_2Brのスピン密度波(SDW)相において、圧力を詳細に変化させた非線形電気伝導の測定により、SDWのスライディングのダイナミクスを電子バンドの1次元性との関わりから調べた。 いずれの圧力でもSDW転移温度T_以下の温度での電流電圧特性において、電場の増加とともにしきい電場E_Tを伴った鋭い伝導度の増大が観測され、ピン止めをはずしたSDWのスライディングが確認された。静止摩擦に相当するしきい電場E_Tの絶対値は低圧領域において、電子バンドの1次元性が小さい(TMTSF)_2PF_6に比べて相当大きいが、圧力を増加させると急速に減少した。E_Tの温度依存は試料によって多少異なるが、典型的な試料では0.3T_近傍の温度で鋭いピークを示し、低温では急激に減少した。これに対してスライディングの動摩擦によって与えられる余剰伝導度は、0.3T_で緩やかなディップを持ち低温で急激に増大した。一方別の試料では、しきい電場の温度変化に明確なピークは見られなかったが、0.3T_付近から急激に減少する振る舞いは共通に観測された。これに対して、余剰伝導度は試料によらずほぼ共通の振る舞いを示した。これらの結果より、SDWのスライディングに対して、静止摩擦と動摩擦は異なるメカニズムにより与えられていることが分かった。さらにこれらの温度依存の振る舞いから、NMR緩和率より示唆される0.3T_でのサブフェーズ移転に関連して、0.3T_以下の温度でSDWは並進運動をし易くなることが明らかになった。このことは(TMTTF)_2X塩のSDW相において示唆されている高温域での電荷密度波(CDW)の共存が、SDWのスライディングのダイナミクスに重要な役割を果たしている可能性が示すものであり、これが1次元性の強い効果であると理解された。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2000 -2000 
    Author : 野村 一成, 松永 悟明, 市村 晃一
     
    カーボンナノチューブのカイラリティーと電子状態の対応を明らかにするため、低温トンネル顕微鏡装置を用いてSTM像観察およびSTS測定を行なった。 前年に引き続き低温でのSTM装置の安定動作化を行い、装置の測定ノイズを低減した。また、新たに導入したガス循環精製装置付き真空グローブボックスを用い、酸素および水分のない雰囲気下でナノチューブ試料を扱うことにより、試料表面の清浄化を行なった。 金属触媒を用いたアーク放電法により作成された単層カーボンナノチューブ試料のSTM像測定を室温で行い、そのバンドル構造を観測した。また、プロファイルからこれらがおよそ1nmの単層カーボンナノチューブからなることを確認した。 STM測定においてバンドルが確認された場所で77KでSTS測定を行い、1.3meV〜1.8meVの有限で平坦な電子状態密度をはさんでVan Hove Singularityの発散的ピークを示す金属ナノチューブの振る舞いを観測した。また、別の場所では0.4meV〜0.6meV程度のギャップを持つ半導体ナノチューブの振る舞いも観測した。これらは、同一のバンドルに属する別のナノチューブで観測されることから、1つのバンドルの中には異なるカイラリティーを持つナノチューブが存在することが明らかになった。さらに、金属ナノチューブのVan Hove Singularityは複数のピークに分裂することも観測したが、これが電子バンドの異方性に起因するかどうかは今後の課題として残された。また、比較的まれにではあるが数10meVのエネルギーに構造を持つトンネルスペクトルを観測した。この原因としては、バンドル内で三角格子を組む金属カーボンナノチューブの電子構造が有力であるが、今後さらに詳細な測定により明らかにされることが期待される。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1996 -1996 
    Author : 市村 晃一, 松永 悟明, 野村 一成
     
    酸化物高温超伝導体Bi_2Sr_2CaCu_2O_8において、低温用走査型トンネル顕微鏡(STM)を用い4.2Kにおいてトンネル分光測定を行った。単結晶側面において測定を行い超伝導ギャップの面内異方性を直接的に調べ、ギャップの対称性を明らかにすることを目的とした。異なる2つの方向からトンネル探針をアプローチし、ノイズの少ないトンネル微分コンダクタンスが得られた。 1.[110]方向(Cu-O-Cu結合方向から45°)でのトンネル ゼロバイアス付近のコンダクタンスは十分に減少し、明確な超伝導ギャップ構造が観測された。そのコンダクタンスカーブは50nm程度の範囲内では場所によらず同一である。コンダクタンスの関数形は以前の測定とほぼ一致する。ギャップの大きさはΔ_=21meVと求まり、以前の結果(Δ_=25meV)より若干小さいが、これは試料依存性と考えられる。 2.[100]方向(Cu-O-Cu結合方向)でのトンネル [110方向でのトンネルとは対照的に、ゼロバイアス付近のコンダクタンスは十分に減少せず、明確なギャップ構造は観測されなかった。方向によりトンネルスペクトルが変化することは、STM測定においてトンネル遷移確率の波数依存性が強いことと、超伝導ギャップが異方的であることを意味する。また、ゼロバイアス付近でコンダクタンスが増加するスペクトルもしばしば観測された。これはいわゆるzero bias conductance peak (ZBCP)に対応するものと思われる。我々の結果ではZBCPは[100]方向でのみ観測されている。ZBCPの存在はギャップにノードがあることを強く示唆する。超伝導ギャップの対称性は、純粋なd-波、もしくはs-波とd-波の混合の対称性である。後者の場合d-波成分がかなり大きいことが結論される。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1995 -1995 
    Author : 松永 悟明
     
    (TMTSF)_2ClO_4はClO_4アニオンの秩序化が試料の冷却速度に依存し、急冷するとスピン密度波状態に転移するが、徐冷すると超伝導状態に転移する。このアニオンの秩序化を利用して冷却速度を変えることにより試料に乱れを導入することができる。本研究では、異方的導体における乱れの影響を明らかにするために、(TMTSF)_2ClO_4の金属及びSDW相において磁気抵抗、磁化率等を詳細に測定した。 その結果、磁化率測定より求めた磁場侵入長の温度依存性より、(TMTSF)_2ClO_4の超伝導相は有限のギャップをもつ超伝導が実現されているとの結論を得た。又、様々な冷却速度における残留抵抗の測定結果より、冷却速度と非磁性不純物散乱の関係を定量的に明らかにした。さらに、金属及びSDW相における磁気抵抗の測定を行った。その結果、SDW相における磁気抵抗の異方性はSDWギャップに伴うホールと電子の有効質量の異方性として定量的に理解できることが分かった。金属相におても大きな磁気抵抗の異方性が観測されたが、その異方性はSDW相とは逆であり、又、その異方性は低温になるにしたがって著しく増大することを見いだした。現在の時点ではこの金属相の磁気抵抗の振舞いに関して適切な解釈をもっていないが、何らかの新しい散乱機構の存在を示唆するものであるのかもしれない。 今後、様々な冷却速度における超伝導相において上部臨界磁場(H_)の測定を行い、ク-パ-対の波動関数の対称性と非磁性不純物の超伝導状態に果す役割をさらに調べるとともに、金属相の磁気抵抗の振舞いを詳細に調べ、低温で増大する磁気抵抗の異方性の起源を明らかにする。又、急冷した場合のスピン密度波相及び徐冷し強磁場を印加した場合の磁場誘起スピン密度波相におけるスピン密度波のダイナミクスを合わせて測定し低次元電子系に特徴的な超伝導相と磁気的相の関連を明らかにする。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1995 -1995 
    Author : 野村 一成, 松永 悟明
     
    (TMTSF)_2X塩のSDW相の電子状態を調べるために、主として非線形電気伝導度測定及びNMR測定を行った。 非線形電気伝導度測定では、寒剤である液体ヘリウム4の排気系を整備し、測定温度域を拡張し1.15Kまでの低温での測定を可能にした。また、低温域におけるジュール加熱の効果を抑えるため、受信系の改良を行い10μsec以下のパルス電流による測定を可能にした。これにより、SDW相での非線形電気伝導度測定を行い、ほぼ全ての温度域において明確なしきい電場を観測した。この結果は、不純物にピン止めされていたSDWが、有限電場の下で古典的な機構によりピン止めをはずしスライディングを開始するモデルにより理解される。一方、低温域でのみ高電場において温度に依存しない大きな非線形電気伝導度が観測された。この新たな電気伝導の機構は量子効果を示唆するものであり、今後さらに詳しく調べる予定である。 NMR測定では、装置の改良を行い測定周波数を50MHzまで広帯域化した。これにより、^1Hのスピン格子緩和率T_1^<-1>の温度変化を周波数を変えながら測定した。この結果、いずれの周波数においてもSDW転移温度より十分低い温度領域でT_1^<-1>の発散的増大を観測した。これによりSDWを二分する新たな転移が磁場によってほとんど変化しないことが明らかになった。また、この転移における局所磁場の揺らぎは、SDW転移におけるものとほぼ同じ周波数依存を持つことも分かった。
  • 低次元有機導体の電子物性
    Date (from‐to) : 1991

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