Discontinuous transition to a superconducting phase
Takumi Sato, Shingo Kobayashi, Yasuhiro Asano
Physical Review B, 2024年10月03日
研究論文（学術雑誌）

Multilocational Majorana zero modes
Yutaro Nagae, Andreas P. Schnyder, Yukio Tanaka, Yasuhiro Asano, Satoshi Ikegaya
Physical Review B, 110, 4, L041110(1), L041110(7), American Physical Society (APS), 2024年07月08日, ［査読有り］
英語, 研究論文（学術雑誌）

Supercurrent reversal in Zeeman-split Josephson junctions
Shu-Ichiro Suzuki, Yasuhiro Asano, Alexander A. Golubov
Physical Review B, 108, 14, 144505(1), 144505(8), American Physical Society (APS), 2023年10月19日, ［査読有り］
英語, 研究論文（学術雑誌）

Fulde-Ferrell-Larkin-Ovchinnikov state in a superconducting thin film attached to a ferromagnetic cluster
Shu-Ichiro Suzuki, Takumi Sato, Alexander A. Golubov, Yasuhiro Asano
Physical Review B, 108, 064509(1), 064509(9), 2023年08月14日, ［査読有り］, ［最終著者］
英語, 研究論文（学術雑誌）

\(\pi \)-phase Shift of the Pair Potential under a Magnetic Cluster
Shu-Ichiro Suzuki, Takumi Sato, Yasuhiro Asano
Proceedings of the 29th International Conference on Low Temperature Physics (LT29), Journal of the Physical Society of Japan, 2023年05月22日
研究論文（国際会議プロシーディングス）

Spin Susceptibility of a J = 3/2 Superconductor
Dakyeong Kim, Takumi Sato, Shingo Kobayashi, Yasuhiro Asano
Journal of the Physical Society of Japan, 92, 5, 054703(1), 054703(9), Physical Society of Japan, 2023年05月15日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）

Nuclear spin relaxation rate of nonunitary Dirac and Weyl superconductors
Koki Maeno, Yuki Kawaguchi, Yasuhiro Asano, Shingo Kobayashi
Physical Review B, 107, 6, 064511(1), 064511(17), American Physical Society (APS), 2023年02月27日, ［査読有り］
英語, 研究論文（学術雑誌）

Odd-frequency Cooper pair around a magnetic impurity
Shu-Ichiro Suzuki, Takumi Sato, Yasuhiro Asano
Physical Review B, 106, 10, 104518(1), 104518(13), American Physical Society (APS), 2022年09月29日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）, 34311520

Quasiparticle on Bogoliubov Fermi Surface and Odd-Frequency Cooper Pair
Dakyeong Kim, Shingo Kobayashi, Yasuhiro Asano
Journal of the Physical Society of Japan, 90, 10, 104708(1), 104708(9), Physical Society of Japan, 2021年10月15日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）

Strong anomalous proximity effect from spin-singlet superconductors
Yasuhiro Asano
Physical Review B, 104, 2, L020502(1), L020502(6), American Physical Society (APS), 2021年07月08日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）

Josephson effect of superconductors with J=3/2 electrons
Yasuhiro Asano
Physical Review B, 103, 18, 184516(1), 184516(9), American Physical Society (APS), 2021年05月27日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）

Odd-parity pairing correlations in a d-wave superconductor
Jaechul Lee, Satoshi Ikegaya, Yasuhiro Asano
Physical Review B, 103, 10, 104509(1), 104509(14), American Physical Society (APS), 2021年03月15日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）

Superconductivity in Cu-doped Bi2Se3 with potential disorder
Yasuhiro Asano
Physical Review B, 102, 2, 024516(1), 024516(10), American Physical Society (APS), 2020年07月17日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）

Identification of spin-triplet superconductivity through a helical-chiral phase transition in Sr2RuO4 thin films
Yasuhiro Asano
Physical Review B, 101, 22, 220501R(1), 220501R(6), American Physical Society (APS), 2020年06月01日, ［査読有り］
英語, 研究論文（学術雑誌）

Nodal Andreev spectra in multi-Majorana three-terminal Josephson junctions
Yasuhiro Asano
Physical Review B, 101, 17, 174506(1), 174506(19), American Physical Society (APS), 2020年05月08日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）

Josephson effect in two-band superconductors
Yasuhiro Asano
Physical Review B, 101, 18, 184601(1), 184601(8), American Physical Society (APS), 2020年05月04日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）

Quasiparticle Spectrum in Mesoscopic Superconducting Junctions with Weak Magnetization
S.-I. Suzuki, A. A. Golubov, Y. Asano, Y. Tanaka
Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019), Journal of the Physical Society of Japan, 2020年03月18日
研究論文（国際会議プロシーディングス）

Unusual Superconducting Proximity Effect in Magnetically Doped Topological Josephson Junctions
Rikizo Yano, Masao Koyanagi, Hiromi Kashiwaya, Kohei Tsumura, Hishiro T. Hirose, Takao Sasagawa, Yasuhiro Asano, Satoshi Kashiwaya
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 89, 3, PHYSICAL SOC JAPAN, 2020年03月, ［査読有り］
英語, 研究論文（学術雑誌）, The transport properties of a topological Josephson junction fabricated from a magnetically doped topological insulator (TI) were investigated. The conductance spectra of the Nb/Fe-Bi2Te2Se/Nb junction below 1 K showed an unusual trident-shaped zero-bias conductance peak with a tiny peak width of similar to 6 mu V. The central peak of the trident peak presents the dc-Josephson current, and the side peaks may reflect an induced unconventional Cooper pairing. Additionally. the critical currents followed inverse to temperature, which may also reflect the presence of an unconventional proximity effect. Furthermore, microwave irradiation drived a drastic change in the conductance spectra from the peak structure into oscillatory ones, a hallmark of the ac-Josephson supercurrent. The current-phase relation of the ac-Josephson effect under high power radiofrequency-irradiation was found to be 4 pi-periodic. The results suggest that the junction based on magnetically doped 3D TIs may realize an unconventional Cooper pairing, thus enabling access to the basic physics of Majorana bound states and unconventional superconductivity.

Proximity effect in a ferromagnetic semiconductor with spin-orbit interactions
Taketoki Yamashita, Jaechul Lee, Tetsuro Habe, Yasuhiro Asano
PHYSICAL REVIEW B, 100, 9, 094501(1), 094501(11), AMER PHYSICAL SOC, 2019年09月, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）, We study theoretically the proximity effect in a ferromagnetic semiconductor with the Rashba spin-orbit interaction. The interplay between the exchange potential and the spin-orbit interactions enriches the symmetry variety of Cooper pairs depending on degree of disorder in a ferromagnet. In the ballistic limit, spin-singlet s-wave Cooper pairs are the most dominant in the presence of strong spin-orbit interaction because the spin-momentum locking stabilizes a Cooper pair consisting of two electrons of time-reversal partner to each other. We will show that the spin-orbit interactions generate equal-spin-triplet p-wave pairs. In the dirty regime, on the other hand, equal-spin-triplet s-wave pairs are dominant because random impurity potentials release the locking. The exchange splitting in the conduction band causes the imbalance between two equal-spin pairing components. In a half-metallic ferromagnet, only an equal-spin pairing component survives and carries the spin-polarized supercurrent. We discuss the effects of the spin-orbit interaction on the Josephson current.

磁性ドープ3Dトポロジカル絶縁体/超伝導体接合における超伝導近接効果
矢野 力三, 津村 公平, 廣瀬 陽代, 小柳 正男, 柏谷 裕美, 浅野 泰寛, 笹川 崇男, 柏谷 聡
日本物理学会講演概要集, 74.1, 1422, 1422, 一般社団法人 日本物理学会, 2019年
日本語

Charge Transport in Unconventional Superconductor Junctions
Yasuhiro Asano, Yukio Tanaka
Springer Series in Materials Science, 286, 117, 145, Springer Verlag, 2019年
英語, 論文集(書籍)内論文, In this section, we discuss charge transport phenomena in junctions consisting of unconventional superconductors. The sign change of the pair potential on the Fermi surface is the essence of unconventional superconductivity and is responsible for the formation of Andreev bound states (ABSs) at a surface of an unconventional superconductor. Since ABSs are localized energetically at the Fermi level, they affect drastically low-energy transport properties such as the differential conductance in a normal-metal/superconductor junction and the Josephson current in a superconductor/insulator/superconductor junction. Today, unconventional superconductivity is considered as a kind of topologically nontrivial state of electrons. We will show that the zero-bias conductance in a disordered junction is described well by a topological invariant defined in terms of a winding number in one-dimensional Brillouin zone. We also discuss the close relationship between odd-frequency Cooper pairs and Majorana Fermions and their consequences on low-energy charge transport.

Effects of phase coherence on local density of states in superconducting proximity structures
Yasuhiro Asano
Physical Review B, 100, 024511(1), 024511(11), 2019年, ［査読有り］
英語, 研究論文（学術雑誌）

Anomalous Nonlocal Conductance as a Fingerprint of Chiral Majorana Edge States
Yasuhiro Asano
Physical Review Letters, 123, 207002(1), 207002(6), 2019年, ［査読有り］
英語, 研究論文（学術雑誌）

Green's-function theory of dirty two-band superconductivity
Yasuhiro Asano, Alexander A. Golubov
Physical Review B, 97, 21, 214508(1), 214508(15), American Physical Society, 2018年06月12日, ［査読有り］, ［筆頭著者, 責任著者］
英語, 研究論文（学術雑誌）, We study the effects of random nonmagnetic impurities on the superconducting transition temperature Tc in a two-band superconductor, where we assume an equal-time spin-singlet s-wave pair potential in each conduction band and the hybridization between the two bands as well as the band asymmetry. In the clean limit, the phase of hybridization determines the stability of two states, called s++ and s+-. The interband impurity scatterings decrease Tc of the two states exactly in the same manner when time-reversal symmetry is preserved in the Hamiltonian. We find that a superconductor with larger hybridization shows more moderate suppression of Tc. This effect can be explained by the presence of odd-frequency Cooper pairs, which are generated by the band hybridization in the clean limit and are broken by impurities.

Symmetry conditions of a nodal superconductor for generating robust flat-band Andreev bound states at its dirty surface
Satoshi Ikegaya, Shingo Kobayashi, Yasuhiro Asano
Physical Review B, 97, 17, 174501(1), 174501(9), American Physical Society, 2018年05月01日, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）, We discuss the symmetry property of a nodal superconductor that hosts robust flat-band zero-energy states at its surface under potential disorder. Such robust zero-energy states are known to induce the anomalous proximity effect in a dirty normal metal attached to a superconductor. A recent study has shown that a topological index NZES describes the number of zero-energy states at the dirty surface of a p-wave superconductor. We generalize the theory to clarify the conditions required for a superconductor that enables NZES≠0. Our results show that NZES≠0 is realized in a topological material that belongs to either the BDI or CII class. We also present two realistic Hamiltonians that result in NZES≠0.

Dirty two-band superconductivity with interband pairing order
Yasuhiro Asano, Akihiro Sasaki, Alexander A. Golubov
New Journal of Physics, 20, 4, 043020(1), 043020(9), Institute of Physics Publishing, 2018年04月01日, ［査読有り］, ［筆頭著者, 責任著者］
英語, 研究論文（学術雑誌）, We study theoretically the effects of random nonmagnetic impurities on the superconducting transition temperature Tc in a two-band superconductor characterized by an equal-time s-wave interband pairing order parameter. Because of the two-band degree of freedom, it is possible to define a spin-triplet s-wave pairing order parameter as well as a spin-singlet s-wave order parameter. The former belongs to odd-band-parity symmetry class, whereas the latter belongs to even-band-parity symmetry class. In a spin-singlet superconductor, Tc is insensitive to the impurity concentration when we estimate the self-energy due to the random impurity potential within the Born approximation. On the other hand in a spin-triplet superconductor, Tc decreases with the increase of the impurity concentration. We conclude that Cooper pairs belonging to odd-band-parity symmetry class are fragile under the random impurity potential even though they have s-wave pairing symmetry.

磁性ドープ3Dトポロジカル絶縁体/超伝導体接合特性の電極間距離依存性
矢野 力三, 津村 公平, 小柳 正男, 柏谷 裕美, 廣瀬 陽代, 浅野 泰寛, 笹川 崇男, 柏谷 聡
日本物理学会講演概要集, 73.2, 788, 788, 一般社団法人 日本物理学会, 2018年
日本語

磁性ドープ3Dトポロジカル絶縁体／超伝導体接合における4π周期ジョセフソン電流の観測
矢野 力三, 小柳 正男, 柏谷 裕美, 津村 公平, 廣瀬 陽代, 浅野 泰寛, 笹川 崇男, 柏谷 聡
日本物理学会講演概要集, 73.1, 1336, 1336, 一般社団法人 日本物理学会, 2018年
日本語

Local impedance on a rough surface of a chiral p-wave superconductor
Yasuhiro Asano
Physical Review B, 98, 134508(1), 134508(16), 2018年, ［査読有り］
英語, 研究論文（学術雑誌）

Tunable-phi Josephson junction with a quantum anomalous Hall insulator
Keimei Sakurai, Satoshi Ikegaya, Yasuhiro Asano
PHYSICAL REVIEW B, 96, 22, 224514(1), 224514(9), AMER PHYSICAL SOC, 2017年12月, ［査読有り］, ［最終著者, 責任著者］
英語, 研究論文（学術雑誌）, We theoretically study the Josephson current in a superconductor/quantum anomalous Hall insulator/superconductor junction by using the lattice Green function technique. When an in-plane external Zeeman field is applied to the quantum anomalous Hall insulator, the Josephson current J flows without a phase difference across the junction theta. The phase shift phi appearing in the current-phase relationship J alpha sin(theta - phi) is proportional to the amplitude of Zeeman fields and depends on the direction ofZeeman fields. Aphenomenological analysis of the Andreev reflection processes explains the physical origin of phi. In a quantum anomalous Hall insulator, time-reversal symmetry and mirror-reflection symmetry are broken simultaneously. However, magnetic mirror-reflection symmetry is preserved. Such characteristic symmetry properties enable us to have a tunable phi junction with a quantum Hall insulator.

Stability of flat zero-energy states at the dirty surface of a nodal superconductor
Satoshi Ikegaya, Yasuhiro Asano
PHYSICAL REVIEW B, 95, 21, 214503(1), 214503(11), AMER PHYSICAL SOC, 2017年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss the stability of highly degenerate zero-energy states that appear at the surface of a nodal superconductor preserving time-reversal symmetry. The existence of such surface states is a direct consequence of the nontrivial topological numbers defined in the restricted Brillouin zones in the clean limit. In experiments, however, potential disorder is inevitable near the surface of a real superconductor, which may lift the high degeneracy at zero energy. We show that an index defined in terms of the chiral eigenvalues of the zero-energy states can be used to measure the degree of degeneracy at zero energy in the presence of potential disorder. We also discuss the relationship between the index and the topological numbers.

Josephson effect in a multiorbital model for Sr2RuO4
Kohei Kawai, Keiji Yada, Yukio Tanaka, Yasuhiro Asano, Alexander A. Golubov, Satoshi Kashiwaya
PHYSICAL REVIEW B, 95, 17, 174518(1), 174518(11), AMER PHYSICAL SOC, 2017年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We study Josephson currents between s-wave/spin-triplet superconductor junctions by taking into account details of the band structures in Sr2RuO4, such as three conduction bands and spin-orbit interactions in the bulk and at the interface. We assume five superconducting order parameters in Sr2RuO4: a chiral p-wave symmetry and four helical p-wave symmetries. We calculate the current-phase relationship I (psi) in these junctions, where. is the macroscopic phase difference between the two superconductors. The results for a chiral p-wave pairing symmetry show that a cos(psi) term appears in the current-phase relation because of time-reversal symmetry (TRS) breaking. On the other hand, this cos(psi) term is absent in the helical pairing states that preserve TRS. We also study the dependence of the maximum Josephson current I-c on an external magnetic flux Phi in a corner junction. The calculated I-c (Phi) obeys I-c (Phi) not equal Ic (-Phi) in a chiral state and I-c (Phi) = I-c (-Phi) in a helical state. We calculate I-c (Phi) in a corner superconducting quantum interference device (SQUID) and a symmetric SQUID geometry. In the latter geometry, I-c (Phi) = I-c (-Phi) is satisfied for all the pairing states and it is impossible to distinguish a chiral state from a helical one. On the other hand, a corner SQUID always gives I-c (Phi) not equal I-c (-Phi) and Ic (Phi) = Ic (-Phi) for a chiral and a helical state, respectively. Experimental tests of these relations in corner junctions and SQUIDs may serve as a tool for unambiguously determining the pairing symmetry in Sr2RuO4.

Spontaneous edge current in a small chiral superconductor with a rough surface
Shu-Ichiro Suzuki, Yasuhiro Asano
PHYSICAL REVIEW B, 94, 15, AMER PHYSICAL SOC, 2016年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We study theoretically the spontaneous edge current in a small chiral superconductor with surface roughness. We obtained self-consistent solutions of the pair potential and the vector potential by solving the quasiclassical Eilenberger equation and the Maxwell equation simultaneously. We then employed them to calculate numerically the spatial distribution of the chiral edge current in a small superconductor. The characteristic behavior of the spontaneous edge current depends strongly on the symmetries of the order parameters such as chiral p-, chiral d-, and chiral f -wave pairing. The edge current is robust under the surface roughness in the chiral p- and chiral d- wave superconductors. In the chiral d- wave case, the surface roughness tends to flip the direction of the chiral current. On the other hand, the edge current in a chiral f -wave superconductor is fragile when there is surface roughness. We also discuss the temperature dependence of a spontaneous magnetization, which is a measurable value in standard experiments.

Degeneracy of Majorana bound states and fractional Josephson effect in a dirty SNS junction
S. Ikegaya, Y. Asano
JOURNAL OF PHYSICS-CONDENSED MATTER, 28, 37, 375702(1), 375702(6), IOP PUBLISHING LTD, 2016年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We theoretically study the stability of more than one Majorana fermion appearing in a p-wave superconductor/dirty normal metal/p-wave superconductor junction in two-dimensions by using the chiral symmetry of a Hamiltonian. At the phase difference across the junction. being pi, we will show that all of the Majorana bound states in the normal metal belong to the same chirality. Due to this pure chiral feature, the Majorana bound states retain their high degree of degeneracy at zero energy even in the presence of a random potential. As a consequence, the resonant transmission of a Cooper pair via the degenerate Majorana bound states carries the Josephson current at phi = pi - 0(+), which explains the fractional current-phase relationship discussed in a number of previous papers.

Quantization of conductance minimum and index theorem
Satoshi Ikegaya, Shu-Ichiro Suzuki, Yukio Tanaka, Yasuhiro Asano
PHYSICAL REVIEW B, 94, 5, AMER PHYSICAL SOC, 2016年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss the minimum value of the zero-bias differential conductance G(min) in a junction consisting of a normal metal and a nodal superconductor preserving time-reversal symmetry. Using the quasiclassical Green function method, we show that G(min) is quantized at (4e(2)/h)N-ZES in the limit of strong impurity scatterings in the normal metal at the zero temperature. The integer N-ZES represents the number of perfect transmission channels through the junction. An analysis of the chiral symmetry of the Hamiltonian indicates that N-ZES corresponds to the Atiyah-Singer index in mathematics.

Influence of the impurity scattering on charge transport in unconventional superconductor junctions
Bo Lu, Pablo Burset, Yasunari Tanuma, Alexander A. Golubov, Yasuhiro Asano, Yukio Tanaka
PHYSICAL REVIEW B, 94, 1, AMER PHYSICAL SOC, 2016年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the influence of nonmagnetic impurity scatterings on the tunneling conductance of a junction consisting of a normal metal and a disordered unconventional superconductor by solving the quasiclassical Eilenberger equation self-consistently. We find that the impurity scatterings in both the Born and the unitary limits affect the formation of the Andreev bound states and modify strongly the tunneling spectra around zero bias. Our results are interpreted well by the appearance of odd-frequency Cooper pairs near the interface and by the divergent behavior of the impurity self-energy. The present paper provides a useful tool to identify the pairing symmetry of unconventional superconductors in experiments.

All-electrical generation and control of odd-frequency s-wave Cooper pairs in double quantum dots
Pablo Burset, Bo Lu, Hiromi Ebisu, Yasuhiro Asano, Yukio Tanaka
PHYSICAL REVIEW B, 93, 20, AMER PHYSICAL SOC, 2016年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We propose an all-electrical experimental setup to detect and manipulate the amplitude of odd-frequency pairing in a double quantum dot. The odd-frequency pair amplitude is induced from the breakdown of orbital symmetry when Cooper pairs are injected in the double dot with electrons in different dots. When the dot levels are aligned with the Fermi energy, i.e., on resonance, nonlocal Andreev processes are directly connected to the presence of odd-frequency pairing. Therefore, their amplitude can be manipulated by tuning the level positions. The detection of nonlocal Andreev processes by conductance measurements contributes a direct proof of the existence of the odd-frequency pair amplitude and is available using current experimental techniques.

22aAY-6 表面が乱れたカイラル超伝導体のエッジ電流
鈴木 修, 浅野 泰寛
日本物理学会講演概要集, 71, 1769, 1769, 一般社団法人日本物理学会, 2016年
日本語

21pBA-7 異常近接効果に起因する分数Josephson効果の微視的理解
池谷 聡, 浅野 泰寛
日本物理学会講演概要集, 71, 1377, 1377, 一般社団法人日本物理学会, 2016年
日本語

奇周波数クーパー対に起因する微小な異方的超伝導体の磁化
鈴木 修, 浅野 泰寛
日本物理学会講演概要集, 71, 1449, 1449, 一般社団法人 日本物理学会, 2016年
日本語,

本研究ではEilenberger方程式とMaxwell方程式を連立させて解く事により、微小な異方的超伝導体の基底状態を調べた。微小な超伝導体の表面には、奇周波数クーパー対が現れる。これら奇周波数クーパー対の磁気不安定性に起因して、微小な超伝導体は、低温で磁化する可能性があることが解った。講演では、磁化する過程と奇周波数クーパー対の役割について議論する。

Spontaneous Edge Current in a Small Chiral Superconductor with a Rough Surface
S.-I. Suzuki, Y. Asano
Physical Review B, 94, 15, 155302(1), 155302(11), 2016年, ［査読有り］
英語, 研究論文（学術雑誌）

Quantization of conductance minimum and index theorem
S. Ikegaya, S.-I. Suzuki, Y. Tanaka, Y. Asano
Physical Review B, 94, 5, 054512(1), 054512(6), 2016年, ［査読有り］
英語, 研究論文（学術雑誌）

Influence of the impurity scattering on charge transport in unconventional superconductor junctions
B. Lu, P. Burset, Y. Tanuma, A. A. Golubov, Y. Asano, Y. Tanaka
Physical Review B, 94, 1, 014504(1), 014504(9), 2016年, ［査読有り］
英語, 研究論文（学術雑誌）

All-electrical generation and control of odd-frequency s-wave Cooper pairs in double quantum dots
P. Burset, B. Lu, H. Ebisu, Y. Asano, Y. Tanaka
Physical Review B, 93, 20, 201402R(1), 201402R(6), 2016年, ［査読有り］
英語, 研究論文（学術雑誌）

Odd-frequency Cooper pairs in two-band superconductors and their magnetic response
Yasuhiro Asano, Akihiro Sasaki
PHYSICAL REVIEW B, 92, 22, 224508(1), 224508(11), AMER PHYSICAL SOC, 2015年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss the appearance of odd-frequency Cooper pairs in two-band superconductors by solving the Gor'kov equation analytically. We introduce the equal-time s-wave pair potentials as realized in MgB2 and iron pnictides. Although the order parameter symmetry is conventional, the band degree of freedom enriches the symmetry variety of pairing correlations. The hybridization and the asymmetry between the two conduction bands induce odd-frequency pairs as a subdominant pairing correlation in the uniform ground state. To study the magnetic response of odd-frequency Cooper pairs, we analyze the Meissner kernel represented by the Gor'kov Green function. In contrast to the even-frequency pairs linked to the pair potential, the induced odd-frequency Cooper pairs indicate a paramagnetic property. We also discuss the relation between the amplitude of the odd-frequency pairing correlation and the stability of superconducting states in terms of the self-consistent equation for the pair potential.

Inversion symmetry of Josephson current as test of chiral domain wall motion in Sr2RuO4
Kohta Saitoh, Satoshi Kashiwaya, Hiromi Kashiwaya, Yasunori Mawatari, Yasuhiro Asano, Yukio Tanaka, Yoshiteru Maeno
PHYSICAL REVIEW B, 92, 10, 100504(1), 100504(6), AMER PHYSICAL SOC, 2015年09月, ［査読有り］
英語, 研究論文（学術雑誌）, Clarifying the chiral domain structure of superconducting Sr2RuO4 has been a long-standing issue in identifying its peculiar topological superconducting state. We evaluated the critical current I-c versus the magnetic field H of Nb/Sr2RuO4 Josephson junctions, changing the junction dimension in expectation of that the number of domains in the junction is controlled. I-c(H) exhibits a recovery from inversion symmetry breaking to invariance when the dimension is reduced to several microns. This inversion invariant behavior indicates the disappearance of domain walls; thus, the size of a single domain is estimated at approximately several microns.

Time-resolved measurements of Cooper-pair radiative recombination in InAs quantum dots
S. S. Mou, H. Irie, Y. Asano, K. Akahane, H. Nakajima, H. Kumano, M. Sasaki, A. Murayama, I. Suemune
JOURNAL OF APPLIED PHYSICS, 118, 7, 073102(1), 073102(7), AMER INST PHYSICS, 2015年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We studied InAs quantum dots (QDs) where electron Cooper pairs penetrate from an adjacent niobium (Nb) superconductor with the proximity effect. With time-resolved luminescence measurements at the wavelength around 1550 nm, we observed luminescence enhancement and reduction of luminescence decay time constants at temperature below the superconducting critical temperature (T-C) of Nb. On the basis of these measurements, we propose a method to determine the contribution of Cooper-pair recombination in InAs QDs. We show that the luminescence enhancement measured below T-C is well explained with our theory including Cooper-pair recombination. (C) 2015 AIP Publishing LLC.

Observability of surface Andreev bound states in a topological insulator in proximity to an s-wave superconductor
M. Snelder, A. A. Golubov, Y. Asano, A. Brinkman
JOURNAL OF PHYSICS-CONDENSED MATTER, 27, 31, 315701(1), 315701(9), IOP PUBLISHING LTD, 2015年08月, ［査読有り］
英語, 研究論文（学術雑誌）, To guide experimental work on the search for Majorana zero-energy modes, we calculate the superconducting pairing symmetry of a three-dimensional topological insulator in combination with an s-wave superconductor. We show how the pairing symmetry changes across different topological regimes. We demonstrate that a dominant p-wave pairing relation is not sufficient to realise a Majorana zero-energy mode useful for quantum computation. Our main result is the relation between odd-frequency pairing and Majorana zero energy modes by using Green functions techniques in three-dimensional topological insulators in the so-called Majorana regime. We discuss thereafter how the pairing relations in the different regimes can be observed in the tunneling conductance of an s-wave proximised three-dimensional topological insulator. We discuss the necessity to incorporate a ferromagnetic insulator to localise the zero-energy bound state to the interface as a Majorana mode.

Optical observation of superconducting density of states in luminescence spectra of InAs quantum dots
S. S. Mou, H. Irie, Y. Asano, K. Akahane, H. Nakajima, H. Kumano, M. Sasaki, A. Murayama, I. Suemune
PHYSICAL REVIEW B, 92, 3, 035308(1), 035308(9), AMER PHYSICAL SOC, 2015年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We study luminescence spectra observed from InAs quantum dots (QDs) embedded in an n-type InGaAs-based heterostructure, where electron Cooper pairs penetrate from an adjacent niobium (Nb) superconductor with the proximity effect. Below the superconducting (SC) critical temperature of Nb, we observe substantial luminescence intensity enhancement and a sharp edge in luminescence spectra of InAs QDs. We explain the observed sharp edge in the luminescence spectra with the proximity effect, that is, with the consideration of opening of SC gap and modification of density of states (DOS) near the electron Fermi level in the n-type semiconductor heterostructure. We demonstrate that the sharp edge luminescence spectra are well reproduced by the SC DOS, with quasiparticle lifetime broadening and a Gaussian distribution of lowest QD state emission lines. We discuss the reason why it has been difficult to observe the sharp edge luminescence spectra in the previous quantum well-based SC light emitting diodes.

Effects of surface roughness on the paramagnetic response of small unconventional superconductors
Shu-Ichiro Suzuki, Yasuhiro Asano
PHYSICAL REVIEW B, 91, 21, 214510(1), 214510(10), AMER PHYSICAL SOC, 2015年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We theoretically study the effects of surface roughness on the magnetic response of small unconventional superconductors by solving the Eilenberger equation for the quassiclassical Green function and the Maxwell equation for the vector potential simultaneously and self-consistently. The paramagnetic phase of spin-singlet d-wave superconducting disks is greatly suppressed by the surface roughness, whereas that of spin-triplet p-wave disks is robust even in the presence of the roughness. This difference derives from the orbital symmetry of paramagnetic odd-frequency Cooper pairs appearing at the surface of the disks. The orbital part of the paramagnetic pairing correlation has p-wave symmetry in the d-wave disks, whereas it has s-wave symmetry in the p-wave disks. Calculating the free energy, we also confirm that the paramagnetic state is more stable than the normal state, which indicates a possibility of detecting the paramagnetic effect in experiments. Indeed, our results are consistent with an experimental finding on high-T-c thin films.

Anomalous proximity effect and theoretical design for its realization
Satoshi Ikegaya, Yasuhiro Asano, Yukio Tanaka
PHYSICAL REVIEW B, 91, 17, 174511(1), 174511(6), AMER PHYSICAL SOC, 2015年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss the stability of zero-energy states appearing in a dirty normal metal attached to a superconducting thin film with Dresselhaus [110] spin-orbit coupling under an in-plane Zeeman field. The Dresselhaus superconductor preserves an additional chiral symmetry and traps more than one zero-energy state at its edges. All the zero-energy states at an edge belong to the same chirality in large Zeeman fields due to the effective p-wave pairing symmetry. The pure chiral nature of the wave function enables the zero-energy states to penetrate the dirty normal metal while retaining their high degree of degeneracy. We prove the perfect Andreev reflection into the dirty normal metal at zero energy.

Odd-frequency superconducting states with different types of Meissner response: Problem of coexistence
Ya. V. Fominov, Y. Tanaka, Y. Asano, M. Eschrig
PHYSICAL REVIEW B, 91, 14, 144514(1), 144514(14), AMER PHYSICAL SOC, 2015年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We consider physical properties of a superconductor with a recently proposed type of odd-frequency pairing that exhibits diamagnetic Meissner response ("odd-dia state"). Such a state was suggested in order to address stability issues arising in an odd-frequency superconducting state with paramagnetic Meissner response ("odd-para state"). Assuming the existence of an odd-dia state (due to a proper retarded interaction), we study its coexistence with an odd-para state. The latter is known to be generated as an induced superconducting component in, e.g., singlet superconductor/ferromagnet proximity structures or triplet superconductor/normal metal systems. Calculating the superfluid density of the mixed odd-para/odd-dia state and the Josephson current between the odd-para and odd-dia states, we find that the expressions for the currents in both cases have nonvanishing imaginary contributions and are therefore unphysical. We show that a realization of the odd-dia state implies the absence of a Hamiltonian description of the system, and suggest that there exists no physically realizable perturbation that could give rise to the spontaneous symmetry breaking necessary for an actual realization of the odd-dia superconducting state.

21pBC-6 Nb/Sr_2RuO_4ジョセフソン接合の磁場応答によるカイラルドメインの検証
斎藤 広大, 柏谷 聡, 柏谷 裕美, 小柳 正男, 馬渡 康徳, 浅野 泰寛, 田仲 由喜夫, 前野 悦輝
日本物理学会講演概要集, 70, 2020, 2020, 一般社団法人日本物理学会, 2015年
日本語

23pAM-6 異常近接効果と多数のマヨラナ・フェルミオンの安定性
池谷 聡, 浅野 泰寛
日本物理学会講演概要集, 70, 1361, 1361, 一般社団法人日本物理学会, 2015年
日本語

22aCT-12 微小な異方的超伝導体の常磁性相とその安定性
鈴木 修, 浅野 泰寛
日本物理学会講演概要集, 70, 1684, 1684, 一般社団法人日本物理学会, 2015年
日本語

Consequences of bulk odd-frequency superconducting states for the classification of Cooper pairs
Yasuhiro Asano, Yakov V. Fominov, Yukio Tanaka
PHYSICAL REVIEW B, 90, 9, 094512(1), 094512(8), AMER PHYSICAL SOC, 2014年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We analyze symmetries and magnetic properties of Cooper pairs appearing as subdominant pairing correlations in inhomogeneous superconductors, on the basis of the quasiclassical Green-function theory. The frequency symmetry, parity, and the type of magnetic response of such subdominant correlations are opposite to those of the dominant pairing correlations in the bulk state. Our conclusion is valid even when we generalize the theory of superconductivity to recently proposed diamagnetic odd-frequency superconductors. As a consequence, Cooper pairs are classified into eight classes in terms of their symmetries and magnetic properties. Anomalous magnetic properties of subdominant components can be probed by studying the Meissner effect.

Andreev Reflection in Weyl Semimetals
Shuhei Uchida, Tetsuro Habe, Yasuhiro Asano
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83, 6, 064711(1), 064711(6), PHYSICAL SOC JAPAN, 2014年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We theoretically study low energy electric transport in a junction consisting of a Weyl semimetal and a metallic superconductor. The characteristic features of the differential conductance depend on the relative directions between the current and the vector connecting the two Weyl points. When the electric current is perpendicular to the vector, the conductance spectra are sensitive to the direction and the amplitude of magnetic moment at the junction interface. This is a direct consequence of the chiral spin configuration on the fermi surface near the Weyl points.

Paramagnetic instability of small topological superconductors
Shu-Ichiro Suzuki, Yasuhiro Asano
PHYSICAL REVIEW B, 89, 18, 184508(1), 184508(7), AMER PHYSICAL SOC, 2014年05月, ［査読有り］
英語, 研究論文（学術雑誌）, The diamagnetism is an essential property of all superconductors. However, we will show that small topological (or unconventional) superconductors can be intrinsically paramagnetic by solving the quasiclassical Eilenberger equation and the Max well equation self-consistently on two-dimensional superconducting disks in weak magnetic fields. Because of the topologically nontrivial character of the wave function, the unconventional superconductors host the zero-energy surface Andreev bound states, which always accompany so-called odd-frequency Cooper pairs. The paramagnetic property of the odd-frequency pairs explains the paramagnetic response of the disks at low temperature.

Three-dimensional symmetry-breaking nontrivial topological states
Tetsuro Habe, Yasuhiro Asano
PHYSICAL REVIEW B, 89, 11, 115203(1), 115203(5), AMER PHYSICAL SOC, 2014年03月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss topological electronic states described by the Dirac Hamiltonian plus an additional one in three dimensions. When the additional Hamiltonian is an element of an Abelian group, electronic states become topologically nontrivial even in the absence of the fundamental symmetries such as the time-reversal symmetry and the particle-hole one. Such symmetry-breaking topological states are characterized by the Chern number defined in the two-dimensional partial Brillouin zone. The topological insulators in Zeeman fields are an example of the symmetry-breaking topological electric state. We show the crossover from the topological insulating phase to the topological semimetal one in strong Zeeman fields.

Bulk-boundary correspondence in Josephson junctions
Jeongmin Yoo, Tetsuro Habe, Yasuhiro Asano
PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 55, 48, 54, ELSEVIER, 2014年01月, ［査読有り］, ［招待有り］
英語, 研究論文（学術雑誌）, We discuss Andreev bound states appearing at the interface between two different superconductors characterized by different nontrivial topological numbers such as one-dimensional winding numbers and Chern numbers. The one-dimensional winding number characterizes d(xy) and p(x) wave superconductors. The Chern number characterizes chiral superconductors. The number of interfacial bound states at the zero-energy is equal to the difference between the topological numbers on either sides of the Josephson junction. We also discuss relation between properties of the Andreev bound states at the zero-energy and features of Josephson current at low temperature. (C) 2013 Elsevier B.V. All rights reserved.

Robustness of Spin-Triplet Pairing and Singlet-Triplet Pairing Crossover in Superconductor/Ferromagnet Hybrids
Shiro Kawabata, Yasuhiro Asano, Yukio Tanaka, Alexander A. Golubov
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82, 12, 124702(1), 124702(9), PHYSICAL SOC JAPAN, 2013年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We have investigated the proximity effect in superconductor/ferromagnet junctions in a systematic manner to discuss the relationship between the zero-energy peak (ZEP) of the local density of states (LDOS) and spin-triplet odd-frequency pairing. By exactly solving the nonlinear Usadel equations, we have found that the ZEP is realized in a wide range of geometrical and material parameters in the case of the noncollinear magnetization. This strongly suggests the robustness of the ZEP induced by spin-triplet odd-frequency pairing in such systems. We also found that the crossover from singlet pairing to triplet pairing can be detected by measuring the F layer thickness dependence of the ZEP height. Furthermore, we show how to observe signatures of spin-triplet odd-frequency pairing and the pairing crossover by LDOS measurement. Our results provide a direct way to experimentally detect signatures of the odd-frequency pairing state.

Robustness of gapless interface states in a junction of two topological insulators
Tetsuro Habe, Yasuhiro Asano
PHYSICAL REVIEW B, 88, 15, 155442(1), 155442(12), AMER PHYSICAL SOC, 2013年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We theoretically study subgap states appearing at the interface between two three-dimensional topological insulators which have different configurations in the spin-orbit interactions from each other. The coupling of spin sigma with momenta p is configured by a material dependent 3 x 3 matrix A as sigma(mu) A(mu)(nu)P(nu). The spectra of the interface subgap states depend on the relative choices of A's in the two topological insulators where the two A are connected by the unitary transformation including the inversion and the rotation in momentum space. The gapless states appear at the interface when the transformation includes the inversion. The two topological insulators can be distinguished by using the topological numbers defined in the two- or one-dimensional partial Brillouin zone, which explains the presence of the gapless interface states. We also discuss the robustness of such gapless states under perturbations breaking the time-reversal symmetry or the band-inversion symmetry.

Charge and spin supercurrents in triplet superconductor-ferromagnet-singlet superconductor Josephson junctions
P. M.R. Brydon, Wei Chen, Yasuhiro Asano, Dirk Manske
Physical Review B - Condensed Matter and Materials Physics, 88, 5, 054509(1), 054509(13), 2013年08月20日, ［査読有り］
英語, 研究論文（学術雑誌）, We study the Josephson effect in a triplet superconductor-ferromagnet- singlet superconductor junction. We show that the interaction of tunneling Cooper pairs with the interface magnetization can permit a Josephson current at the lowest order of a tunneling Hamiltonian perturbation theory. Two conditions must be satisfied for this to occur: The magnetization of the ferromagnet has a component parallel to the d vector of the triplet superconductor, and the gaps of the superconductors have the same parity with respect to the interface momentum. The resulting charge current displays an unconventional dependence on the orientation of the magnetic moment and the phase difference. This is accompanied by a phase-dependent spin current in the triplet superconductor, while a phase-independent spin current is always present. The tunneling perturbation theory predictions are confirmed using a numerical Green's function method. An analytical treatment of a one-dimensional junction demonstrates that our conclusions are robust far away from the tunneling regime and reveals signatures of the unconventional Josephson effect in the critical currents. © 2013 American Physical Society.

Charge and spin supercurrents in triplet superconductor-ferromagnet-singlet superconductor Josephson junctions
P. M. R. Brydon, Wei Chen, Yasuhiro Asano, Dirk Manske
PHYSICAL REVIEW B, 88, 5, AMER PHYSICAL SOC, 2013年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the Josephson effect in a triplet superconductor-ferromagnet-singlet superconductor junction. We show that the interaction of tunneling Cooper pairs with the interface magnetization can permit a Josephson current at the lowest order of a tunneling Hamiltonian perturbation theory. Two conditions must be satisfied for this to occur: The magnetization of the ferromagnet has a component parallel to the d vector of the triplet superconductor, and the gaps of the superconductors have the same parity with respect to the interface momentum. The resulting charge current displays an unconventional dependence on the orientation of the magnetic moment and the phase difference. This is accompanied by a phase-dependent spin current in the triplet superconductor, while a phase-independent spin current is always present. The tunneling perturbation theory predictions are confirmed using a numerical Green's function method. An analytical treatment of a one-dimensional junction demonstrates that our conclusions are robust far away from the tunneling regime and reveals signatures of the unconventional Josephson effect in the critical currents.

Gapped Energy Spectra around the Dirac Node at the Surface of a Three-Dimensional Topological Insulator in the Presence of the Time-Reversal Symmetry
Tetsuro Habe, Yasuhiro Asano
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82, 6, 064704(1), 064704(5), PHYSICAL SOC JAPAN, 2013年06月, ［査読有り］
英語, 研究論文（学術雑誌）, . We discuss the excitation spectra around the Dirac node on a surface of a three-dimensional topological insulator. By using the diagrammatic expansion, we show that the coupling of an electron with the gauge field in the presence of impurity scatterings opens a gap around the Dirac node. The results are consistent with a recent experimental finding by Sato et al. [Nat. Phys. 7 (2011) 840]. We also discuss the consistency between the present results and the bulk-boundary correspondence of the topological insulator in the presence of time reversal symmetry. The conclusion can be applied to any two-dimensional massless fermions.

Majorana fermions and odd-frequency Cooper pairs in a normal-metal nanowire proximity-coupled to a topological superconductor
Yasuhiro Asano, Yukio Tanaka
PHYSICAL REVIEW B, 87, 10, 104513(1), 104513(10), AMER PHYSICAL SOC, 2013年03月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss a strong relationship between Majorana fermions and odd-frequency Cooper pairs which appear at a disordered normal (N) nanowire attached to a topologically nontrivial superconducting (S) one. The transport properties in superconducting nanowire junctions show universal behaviors irrespective of the degree of disorder: the quantized zero-bias differential conductance at 2e(2)/h in NS junction and the fractional current-phase (J-phi) relationship of the Josephson effect in SNS junction J alpha sin(phi/2). Such behaviors are exactly the same as those found in the anomalous proximity effect of odd-parity spin-triplet superconductors. We show that the odd-frequency pairs exist wherever the Majorana fermions stay. DOI: 10.1103/PhysRevB.87.104513

Anomalous surface impedance in a normal-metal/superconductor junction with a spin-active interface
Yasuhiro Asano, Masahiro Ozaki, Tetsuro Habe, Alexander A. Golubov, Yukio Tanaka
PHYSICAL REVIEW B, 86, 2, 024510, AMER PHYSICAL SOC, 2012年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss the surface impedance (Z = R - iX) of a normal-metal/superconductor proximity structure taking into account the spin-dependent potential at the junction interface. Because of the spin-mixing transport at the interface, odd-frequency spin-triplet s-waveCooper pairs penetrate into the normal metal and cause the anomalous response to electromagnetic fields. At low temperature, the local impedance at a surface of the normal metal shows the nonmonotonic temperature dependence and the anomalous relation R > X. We also discuss a possibility of observing such anomalous impedance in experiments.

Interface metallic states between a topological insulator and a ferromagnetic insulator
Tetsuro Habe, Yasuhiro Asano
Physical Review B - Condensed Matter and Materials Physics, 85, 19, 195325.1-195325.8, 2012年05月29日, ［査読有り］
英語, 研究論文（学術雑誌）, We study electronic structures at an interface between a topological insulator and a ferromagnetic insulator by using a three-dimensional two-band model. In usual ferromagnetic insulators, the exchange potential is much larger than the bulk gap size in the topological insulators and electronic structures are asymmetric with respect to the Fermi level. In such situation, we show that unusual metallic states appear under the magnetic moment pointing the perpendicular direction to the junction plane, which cannot be described by the two-dimensional effective model around the Dirac point. When the magnetic moment is in the parallel direction to the plane, the number of Dirac cones becomes even integers. The conclusions obtained in analytical calculations are confirmed by numerical simulations on tight-binding lattice. © 2012 American Physical Society.

Interface metallic states between a topological insulator and a ferromagnetic insulator
Tetsuro Habe, Yasuhiro Asano
PHYSICAL REVIEW B, 85, 19, 195325, AMER PHYSICAL SOC, 2012年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We study electronic structures at an interface between a topological insulator and a ferromagnetic insulator by using a three-dimensional two-band model. In usual ferromagnetic insulators, the exchange potential is much larger than the bulk gap size in the topological insulators and electronic structures are asymmetric with respect to the Fermi level. In such situation, we show that unusual metallic states appear under the magnetic moment pointing the perpendicular direction to the junction plane, which cannot be described by the two-dimensional effective model around the Dirac point. When the magnetic moment is in the parallel direction to the plane, the number of Dirac cones becomes even integers. The conclusions obtained in analytical calculations are confirmed by numerical simulations on tight-binding lattice.

Photon-pair generation based on superconductivity
Ikuo Suemune, Hirotaka Sasakura, Yasuhiro Asano, Hidekazu Kumano, Ryotaro Inoue, Kazunori Tanaka, Tatsushi Akazaki, Hideaki Takayanagi
IEICE ELECTRONICS EXPRESS, 9, 14, 1184, 1200, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, 2012年, ［査読有り］
英語, 研究論文（学術雑誌）, Superconductivity and optoelectronics have developed almost independently and had very rare interactions with each other in science and technologies. However recent interdisciplinary research opens up the potential for developing new optoelectronic devices. This review paper presents our recent theoretical and experimental demonstrations that superconductivity significantly modifies and accelerates photon generation processes. We have prepared superconducting light emitting diodes (LEDs) emitting at similar to 1.6-mu m optical-fiber communication band for the experimental demonstrations. This new-type LED operation is based on a unique physics related to Cooper-pair interband transition in a semiconductor, and further research leads to the solid-state simultaneously generated photon-pair sources for the potential application in quantum information and communication.

Theory of Proximity Effect in Ferromagnet/Superconductor Heterostructures in the Presence of Spin Dependent Interfacial Phase Shift
Daisuke Yoshizaki, Alexander A. Golubov, Yukio Tanaka, Yasuhiro Asano
JAPANESE JOURNAL OF APPLIED PHYSICS, 51, 1, 010108.1-010108.9, IOP PUBLISHING LTD, 2012年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the proximity effect and charge transport in ferromagnet (F)/superconductor (S) and S/F/I/F/S junctions (where I is insulator) by taking into account simultaneously exchange field in F and spin-dependent interfacial phase shifts (SDIPS) at the F/S interface. We solve the Usadel equations using extended Kupriyanov-Lukichev boundary conditions which include SDIPS, where spin-independent part of tunneling conductance G(T) and spin-dependent one G(phi) coexist. The resulting local density of states (LDOS) in a ferromagnet depends both on the exchange energy E-ex and G(phi)/G(T). We show that the magnitude of zero-temperature gap and the height of zero-energy LDOS have a non-monotonic dependence on G(phi)/G(T). We also calculate Josephson current in S/F/I/F/S junctions and show that crossover from 0-state to pi. (C) 2012 The Japan Society of Applied Physics

Cooper-Pair Radiative Recombination in Semiconductor Heterostructures: Impact on Quantum Optics and Optoelectronics
Ikuo Suemune, Hirotaka Sasakura, Yujiro Hayashi, Kazunori Tanaka, Tatsushi Akazaki, Yasuhiro Asano, Ryotaro Inoue, Hideaki Takayanagi, Eiichi Hanamura, Jae-Hoon Huh, Claus Hermannstaedter, Satoru Odashima, Hidekazu Kumano
JAPANESE JOURNAL OF APPLIED PHYSICS, 51, 1, 010114.1-010114.10, JAPAN SOC APPLIED PHYSICS, 2012年01月, ［査読有り］
英語, 研究論文（学術雑誌）, The injection of Cooper pairs into a normal medium such as a semiconductor is known as the proximity effect at the superconductor/normal interface. We confirm this injection as well as the contribution of Cooper pairs to a drastic enhancement of inter-band optical transitions in semiconductor heterostructures. In this paper we investigate and clarify the relation of internal quantum efficiencies and radiative lifetimes in Cooper-pair light emitting diodes (CP-LEDs). A quantitative description of the dynamic photon generation processes is given, and the contribution of the Cooper-pair recombination relative to normal-electron recombination in CP-LEDs is discussed in detail. (C) 2012 The Japan Society of Applied Physics

Cooper-pair Radiative Recombination in Semiconductors and Its Superconductivity Impact on Optoelectronics and Quantum Optics
I. Suemune, H. Sasakura, Y. Hayashi, K. Tanaka, T. Akazaki, Y. Asano, R. Inoue, H. Takayanagi, E. Hanamura, J.-H. Huh, C. Hermannstädter, S. Odashima, H. Kumano
Jpn. J. App. Phys., 51, 010114, 2012年, ［査読有り］
英語, 研究論文（学術雑誌）

Enhanced Photon Generation in a Nb/n - InGaAs/p - InP Superconductor/Semiconductor-Diode Light Emitting Device
H. Sasakura, S. Kuramitsu, Y. Hayashi, K. Tanaka, T. Akazaki, E. Hanamura, R. Inoue, H. Takayanagi, Y. Asano, C. Hermannstaedter, H. Kumano, I. Suemune
PHYSICAL REVIEW LETTERS, 107, 15, 157403, AMER PHYSICAL SOC, 2011年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We experimentally demonstrate Cooper pairs' drastic enhancement of the band-to-band radiative recombination rate in a semiconductor. Electron Cooper pairs injected from a superconducting electrode into an active layer by the proximity effect recombine with holes injected from a p-type electrode. The recombination of a Cooper pair with p-type carriers dramatically increases the photon generation probability of a light-emitting diode in the optical-fiber communication band. The measured radiative decay time rapidly decreases with decreasing temperature below the superconducting transition temperature of the niobium electrodes. Our results indicate the possibility to open up new interdisciplinary fields between superconductivity and optoelectronics.

Josephson effect in noncentrosymmetric superconductor junctions
Yasuhiro Asano, Satoshi Yamano
PHYSICAL REVIEW B, 84, 6, 064526, AMER PHYSICAL SOC, 2011年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss the Josephson current between two noncentrosymmetric superconductors. The coexistence of superconducting order parameters between the spin-singlet Delta(S) and the helical p-wave spin-triplet Delta(T) enriches a variety of low-temperature behavior of the Josephson current depending on their relative amplitudes. We will show that characteristic behaviors of the Josephson current for Delta(S) > Delta(T) are clearly different from those for Delta(S) < Delta(T). The topologically protected zero-energysurface bound states are responsible for the clear difference. We conclude that the Josephson current reflects well the character of the topological surface states and the pairing symmetry of noncentrosymmetric superconductors.

Unconventional Surface Impedance of a Normal-Metal Film Covering a Spin-Triplet Superconductor Due to Odd-Frequency Cooper Pairs
Yasuhiro Asano, Alexander A. Golubov, Yakov V. Fominov, Yukio Tanaka
PHYSICAL REVIEW LETTERS, 107, 8, 087001, AMER PHYSICAL SOC, 2011年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss the dynamic response of odd-frequency Cooper pairs to an electromagnetic field. By using the quasiclassical Green function method, we calculate the impedance (Z = R - iX) of a normal-metal thin film which covers a superconductor. In contrast with the standard relation ( i.e., R << X), the impedance in spin-triplet proximity structures shows anomalous behavior ( i.e., R > X) in the low frequency limit. This unusual relation is a result of the penetration of odd-frequency pairs into the normal metal and reflects the negative Cooper pair density.

Spin Josephson effect with a single superconductor
P. M. R. Brydon, Yasuhiro Asano, Carsten Timm
PHYSICAL REVIEW B, 83, 18, 180504, AMER PHYSICAL SOC, 2011年05月, ［査読有り］
英語, 研究論文（学術雑誌）, A thin ferromagnetic layer on a bulk equal-spin-pairing triplet superconductor is shown to mediate a Josephson coupling between the spin up arrow and down arrow condensates of the superconductor. By deriving analytic expressions for the bound states at the triplet superconductor-ferromagnet interface, we show that this spin Josephson effect establishes an effective anisotropy axis in the ferromagnetic layer. The associated Josephson spin current is predicted to cause a measurable precession of the magnetization about the vector order parameter of the triplet superconductor.

Theory of quantum transport in Josephson junctions with a ferromagnetic insulator
Shiro Kawabata, Yasuhiro Asano
Fizika Nizkikh Temperatur (Kharkov), 36, 10-11, 1143, 1148, 2010年10月
研究論文（学術雑誌）, We investigate the Josephson transport through ferromagnetic insulators (FIs) by taking into account the band structure of FIs explicitly. Using the recursive Green's function method, we found the formation of a π-junction in such systems. Moreover the atomic-scale 0-π oscillation is induced by increasing the thickness of FI and its oscillation period is universal, i.e., just single atomic layer. Based on these results, we show that stable π-state can be realized in junctions based on high-Tc superconductors with La2BaCuO5 barrier. Such FI-based Josephson junctions may become an element in the architecture of future quantum computers. © Shiro Kawabata and Yasuhiro Asano, 2010.

Theory of quantum transport in Josephson junctions with a ferromagnetic insulator
Shiro Kawabata, Yasuhiro Asano
LOW TEMPERATURE PHYSICS, 36, 10-11, 915, 919, AMER INST PHYSICS, 2010年10月
英語, 研究論文（学術雑誌）, We investigate Josephson transport through ferromagnetic insulators (FIs) taking the band structure of the FIs explicitly into account. Using a recursive Green function method, we find that a pi-junction is formed in this type of system. Moreover, an atomic-scale 0-pi oscillation is induced by increasing the thickness of an FI and its oscillation period is universal, exactly equal to a single atomic layer. Based on these results, we show that a stable pi-state can be realized in junctions based on high-T-c superconductors with a La2BaCuO5 barrier. Such FI-based Josephson junctions may become an element in the architecture of future quantum computers. (C) 2010 American Institute of Physics. [doi:10.1063/1.3515524]

DC Current Driven Critical Current Variation in Sr2RuO4-Ru Junction Proved by Local Transport Measurements
Hiroshi Kambara, Tetsuro Matsumoto, Hiromi Kashiwaya, Satoshi Kashiwaya, Hiroshi Yaguchi, Yasuhiro Asano, Yukio Tanaka, Yoshiteru Maeno
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 79, 7, 074708.1-074708.5, PHYSICAL SOC JAPAN, 2010年07月, ［査読有り］
英語, 研究論文（学術雑誌）, To search for new evidence of the chiral p-wave superconducting domain in Sr2RuO4, we investigated the unconventional local transport characteristics of a microfabricated Sr2RuO4-Ru eutectic junction. We found that the anomalous hysteresis in voltage-current characteristics [as reported in Kambara et al.: Phys. Rev. Lett. 101 (2008) 267003] is strongly affected by dc currents, but not by magnetic fields. This suggests that dc current acts as a driving force to move chiral p-wave domain walls; a domain wall trapped at a pinning potential is forced to shift to the next stable position, thereby forming a larger critical current path and resulting in the anomalous hysteresis.

Tunneling between Two Helical Superconductors via Majorana Edge Channels
Yasuhiro Asano, Yukio Tanaka, Naoto Nagaosa
PHYSICAL REVIEW LETTERS, 105, 5, 056402.1-056402.4, AMER PHYSICAL SOC, 2010年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss electric transport through a point contact which bridges Majorana fermion modes appearing at edges of two helical superconductors. The contents focus on the effects of interference and interaction unique to the Majorana fermions and the role of spin-orbit interaction (SOI). Besides the Josephson current, the quasiparticle conductance depends sensitively on the phase difference and relative helicity between the two superconductors. The interaction among the Majorana fermions causes the power-law temperature dependences of conductance for various tunneling channels. Especially, in the presence of SOI, the conductance always increases as the temperature is lowered.

Josephson pi State in a Ferromagnetic Insulator
Shiro Kawabata, Yasuhiro Asano, Yukio Tanaka, Alexander A. Golubov, Satoshi Kashiwaya
PHYSICAL REVIEW LETTERS, 104, 11, 117002.1-117002.4, AMER PHYSICAL SOC, 2010年03月, ［査読有り］
英語, 研究論文（学術雑誌）, We predict anomalous atomic-scale 0-pi transitions in a Josephson junction with a ferromagnetic-insulator (FI) barrier. The ground state of such junction alternates between 0 and pi states when thickness of FI is increasing by a single atomic layer. We find that the mechanism of the 0-pi transition can be attributed to thickness-dependent phase shifts between the wave numbers of electrons and holes in FI. Based on these results, we show that a stable pi state can be realized in junctions based on high-T(c) superconductors with a La(2)BaCuO(5) barrier.

A Cooper-Pair Light-Emitting Diode: Temperature Dependence of Both Quantum Efficiency and Radiative Recombination Lifetime
Ikuo Suemune, Yujiro Hayashi, Shuhei Kuramitsu, Kazunori Tanaka, Tatsushi Akazaki, Hirotaka Sasakura, Ryotaro Inoue, Hideaki Takayanagi, Yasuhiro Asano, Eiichi Hanamura, Satoru Odashima, Hidekazu Kumano
APPLIED PHYSICS EXPRESS, 3, 5, 054001.1-054001.3, JAPAN SOC APPLIED PHYSICS, 2010年, ［査読有り］
英語, 研究論文（学術雑誌）, A light-emitting diode (LED) in the optical-fiber communication band showed special features after replacing the n-type electrode with niobium (Nb) superconducting metal. Nb electrodes prepared on an InGaAs-based semiconductor surface formed a superconductor/semiconductor/superconductor junction, and the current-voltage characteristics exhibited both DC and AC Josephson junction properties. This was a result of the injection of electron Cooper-pairs into the n-InGaAs active layer of an LED. The drastic enhancement of the electroluminescence output observed below the Nb superconducting critical temperature, T(c), demonstrates the active role of electron Cooper-pairs in radiative recombination. Lifetime measurements of this LED and accurate evaluation of the luminescence output made it possible to estimate the radiative recombination lifetimes. A theoretical formula derived for the Cooper-pair radiative recombination accurately describes both the measured steep reduction of the radiative recombination lifetime and the observed enhancement of the internal quantum efficiency below Tc. This work will assist the development of interdisciplinary physics and new applications in superconductivity and optoelectronics. (C) 2010 The Japan Society of Applied Physics

Luminescence of a Cooper Pair
Yasuhiro Asano, Ikuo Suemune, Hideaki Takayanagi, Eiichi Hanamura
PHYSICAL REVIEW LETTERS, 103, 18, 187001.1-187001.4, AMER PHYSICAL SOC, 2009年10月, ［査読有り］
英語, 研究論文（学術雑誌）, This Letter theoretically discusses the photon emission spectra of a superconducting p-n junction. On the basis of the second order perturbation theory for electron-photon interaction, we show that the recombination of a Cooper pair with two p-type carriers causes enhancement of the luminescence intensity. The calculated results of photon emission spectra explain characteristic features of observed signal in an recent experiment. Our results indicate high functionalities of superconducting light-emitting devices.

Parity violation in a single domain of spin-triplet Sr2RuO4 superconductors
H. Nobukane, K. Inagaki, K. Ichimura, K. Yamaya, S. Takayanagi, I. Kawasaki, K. Tenya, H. Amitsuka, K. Konno, Y. Asano, S. Tanda
SOLID STATE COMMUNICATIONS, 149, 29-30, 1212, 1215, PERGAMON-ELSEVIER SCIENCE LTD, 2009年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We observed an unconventional parity-violating vortex in single domain Sr2RuO4 single crystals using a transport measurement. The current-voltage characteristics of submicron Sr2RuO4 show that the induced voltage has anomalous components which are even functions of the bias current. The results may suggest that the vortex itself has a helical internal structure characterized by a Hopf invariant (a topological invariant). We also discuss that the hydrodynamics of such a helical vortex causes the parity violation to retain the topological invariant. (C) 2009 Elsevier Ltd. All rights reserved.

Odd-frequency pairing in superconducting heterostructures
A. A. Golubov, Y. Tanaka, Y. Asano, Y. Tanuma
JOURNAL OF PHYSICS-CONDENSED MATTER, 21, 16, 164208,1-8, IOP PUBLISHING LTD, 2009年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We review the theory of odd-frequency pairing in superconducting heterostructures, where an odd-frequency pairing component is induced near interfaces. A general description of the superconducting proximity effect in a normal metal or a ferromagnet attached to an unconventional superconductor (S) is given within quasiclassical kinetic theory for various types of symmetry state in S. Various possible symmetry classes in a superconductor are considered which are consistent with the Pauli principle: even-frequency spin-singlet even-parity (ESE) state, even-frequency spin-triplet odd-parity (ETO) state, odd-frequency spin-triplet even-parity (OTE) state and odd-frequency spin-singlet odd-parity (OSO) state. As an example, we consider a junction between a diffusive normal metal (DN) and a p-wave superconductor (even-frequency spin-triplet odd-parity symmetry), where the pairing amplitude in DN belongs to an odd-frequency spin-triplet even-parity symmetry class. We also discuss the manifestation of odd-frequency pairing in conventional superconductor/normal (S/N) proximity systems and its relation to the classical McMillan-Rowell oscillations.

Anomalous Transport through the p-Wave Superconducting Channel in the 3-K Phase of Sr2RuO4
Hiroshi Kambara, Satoshi Kashiwaya, Hiroshi Yaguchi, Yasuhiro Asano, Yukio Tanaka, Yoshiteru Maeno
PHYSICAL REVIEW LETTERS, 101, 26, 267003.1-267003.4, AMER PHYSICAL SOC, 2008年12月, ［査読有り］
英語, 研究論文（学術雑誌）, Using microfabrication techniques, we extracted individual channels of 3-kelvin (3-K) phase superconductivity in Sr2RuO4-Ru eutectic systems and confirmed odd-parity superconductivity in the 3-K phase, similar to pure Sr2RuO4. Unusual hysteresis in the differential resistance-current and voltage-current characteristics observed below 2 K indicates the internal degrees of freedom of the superconducting state. A possible origin of the hysteresis is current-induced chiral-domain-wall motion due to the chiral p-wave state.

Electron transport in a ferromagnet-superconductor junction on graphene
Yasuhiro Asano, Toshihiro Yoshida, Yukio Tanaka, Alexander A. Golubov
Physical Review B - Condensed Matter and Materials Physics, 78, 1, 014514, 2008年07月18日, ［査読有り］
英語, 研究論文（学術雑誌）, In a usual ferromagnet connected with a superconductor, the exchange potential suppresses the superconducting pairing correlation. We show that this common knowledge does not hold in a ferromagnet-superconductor junction on a graphene. When the chemical potential of a graphene is close to the conical point of energy dispersion, the exchange potential rather assists the charge transport through a junction interface. The loose-bottomed electric structure causes this unusual effect. © 2008 The American Physical Society.

Flat rotation curves in Chern-Simons modified gravity
Kohkichi Konno, Toyoki Matsuyama, Yasuhiro Asano, Satoshi Tanda
PHYSICAL REVIEW D, 78, 2, 024037, AMER PHYSICAL SOC, 2008年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We investigate the spacetime of a slowly rotating black hole in the Chern-Simons modified gravity. The long range feature of frame-dragging effect under the Chern-Simon gravity well explains the flat rotation curves of galaxies which is a central evidence of dark matter. Our solution provides a different scenario of rotating space from Godel's solution.

Shape of Cooper pairs in a normal-metal/superconductor junction
Yukio Tanaka, Yasuhiro Asano, Alexander A. Golubov
PHYSICAL REVIEW B, 77, 22, 220504, AMER PHYSICAL SOC, 2008年06月, ［査読有り］
英語, 研究論文（学術雑誌）, In s-wave superconductors the Cooper pair wave function is isotropic in momentum space. This property may also be expected for Cooper pairs entering a normal metal from a superconductor due to the proximity effect. We show, however, that such a deduction is incorrect and the pairing function in a normal metal is surprisingly anisotropic because of quasiparticle interference. We calculate angle-resolved quasiparticle density of states in NS bilayers which reflects such anisotropic shape of the pairing function. We also propose a magnetotunneling spectroscopy experiment which could confirm our predictions.

Quantum transport in a normal metal/odd-frequency superconductor junction
Jacob Linder, Takehito Yokoyama, Yukio Tanaka, Yasuhiro Asano, Asle Sudbø
Physical Review B - Condensed Matter and Materials Physics, 77, 17, 174505, 2008年05月06日
英語, 研究論文（学術雑誌）, Recent experimental results indicate the possible realization of a bulk odd-frequency superconducting state in the compounds CeCu2 Si2 and CeRhIn5. Motivated by this, we present a study of the quantum transport properties of a normal metal/odd-frequency superconductor junction in a search for probes to unveil the odd-frequency symmetry. From the Eliashberg equations, we perform a quasiclassical approximation to account for the transport formalism of an odd-frequency superconductor with the Keldysh formalism. Specifically, we consider the tunneling charge conductance and the tunneling thermal conductance. We qualitatively find distinct behavior in the odd-frequency case compared to the conventional even-frequency case in both the electrical and thermal current. This serves as a useful tool to identify the possible existence of a bulk odd-frequency superconducting state. © 2008 The American Physical Society.

Quantum transport in a normal metal/odd-frequency superconductor junction
Jacob Linder, Takehito Yokoyama, Yukio Tanaka, Yasuhiro Asano, Asle Sudbo
PHYSICAL REVIEW B, 77, 17, AMER PHYSICAL SOC, 2008年05月, ［査読有り］
英語, 研究論文（学術雑誌）, Recent experimental results indicate the possible realization of a bulk odd-frequency superconducting state in the compounds CeCU2Si2 and CeRhIn5. Motivated by this, we present a study of the quantum transport properties of a normal metal/odd-frequency superconductor junction in a search for probes to unveil the odd-frequency symmetry. From the Eliashberg equations, we perform a quasiclassical approximation to account for the transport formalism of an odd-frequency superconductor with the Keldysh formalism. Specifically, we consider the tunneling charge conductance and the tunneling thermal conductance. We qualitatively find distinct behavior in the odd-frequency case compared to the conventional even-frequency case in both the electrical and thermal current. This serves as a useful tool to identify the possible existence of a bulk odd-frequency superconducting state.

Strongly spin-polarized current generated in a Zeeman-split superconductor
J. Linder, T. Yokoyama, Y. Tanaka, Y. Asano, A. Sudbø
Physical Review B, 78, 14, 014516_1-5, 14516, American Physical Society, 2008年, ［査読有り］
英語, 研究論文（学術雑誌）

Evolution of Chiral Superconducting Order in 3-K Phase of Sr2RuO4　　　　　　　　　　　　　　　
H. Kambara, S. Kashiwaya, H. Yaguchi, Y. Asano, Y. Tanaka, Y. Maeno
Physical Review Letters, 101, 267003_1-4, 2008年, ［査読有り］
英語, 研究論文（学術雑誌）

Electron Transport of a Ferromagnet-Superconductor junction on Graphene　　　　　　　　　　　　　　　
Y. Asano, T. Yoshida, Y. Tanaka, A. A. Golubov
Physical Review B, 14, 014516_1-5, 2008年, ［査読有り］
英語, 研究論文（学術雑誌）

Odd-frequency pairs and Josephson current through a strong ferromagnet
Yasuhiro Asano, Yuki Sawa, Yukio Tanaka, Alexander A. Golubov
Physical Review B - Condensed Matter and Materials Physics, 76, 22, 224525, 2007年12月27日
英語, 研究論文（学術雑誌）, We study Josephson current in superconductor/diffusive ferromagnet/ superconductor junctions by using the recursive Green function method. When the exchange potential in a ferromagnet is sufficiently large compared to the pair potential in a superconductor, an ensemble average of Josephson current is much smaller than its mesoscopic fluctuations. The Josephson current vanishes when the exchange potential is extremely large so that a ferromagnet is half-metallic. Spin-flip scattering at junction interfaces drastically changes the characteristic behavior of Josephson current. In addition to spin-singlet Cooper pairs, equal-spin triplet pairs penetrate into a half metal. Such equal-spin pairs have an unusual symmetry property called odd-frequency symmetry and carry the Josephson current through a half metal. The penetration of odd-frequency pairs into a half metal enhances the low energy quasiparticle density of states, which could be detected experimentally by scanning tunneling spectroscopy. We will also show that odd-frequency pairs in a half metal cause a nonmonotonic temperature dependence of the critical Josephson current. © 2007 The American Physical Society.

Odd-frequency pairs and Josephson current through a strong ferromagnet
Yasuhiro Asano, Yuki Sawa, Yukio Tanaka, Alexander A. Golubov
PHYSICAL REVIEW B, 76, 22, AMER PHYSICAL SOC, 2007年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We study Josephson current in superconductor/diffusive ferromagnet/superconductor junctions by using the recursive Green function method. When the exchange potential in a ferromagnet is sufficiently large compared to the pair potential in a superconductor, an ensemble average of Josephson current is much smaller than its mesoscopic fluctuations. The Josephson current vanishes when the exchange potential is extremely large so that a ferromagnet is half-metallic. Spin-flip scattering at junction interfaces drastically changes the characteristic behavior of Josephson current. In addition to spin-singlet Cooper pairs, equal-spin triplet pairs penetrate into a half metal. Such equal-spin pairs have an unusual symmetry property called odd-frequency symmetry and carry the Josephson current through a half metal. The penetration of odd-frequency pairs into a half metal enhances the low energy quasiparticle density of states, which could be detected experimentally by scanning tunneling spectroscopy. We will also show that odd-frequency pairs in a half metal cause a nonmonotonic temperature dependence of the critical Josephson current.

Conductance spectroscopy of spin-triplet superconductors
Yasuhiro Asano, Yukio Tanaka, Alexander A. Golubov, Satoshi Kashiwaya
PHYSICAL REVIEW LETTERS, 99, 6, 067005.1-067005.4, AMER PHYSICAL SOC, 2007年08月
英語, 研究論文（学術雑誌）, We propose a novel experiment to identify the symmetry of superconductivity on the basis of theoretical results for differential conductance of a normal metal connected to a superconductor. The proximity effect from the superconductor modifies the conductance of the remote current depending remarkably on the pairing symmetry: spin singlet or spin triplet. The clear-cut difference in the conductance is explained by symmetry of Cooper pairs in a normal metal with respect to frequency. In the spin-triplet case, the anomalous transport is realized due to an odd-frequency symmetry of Cooper pairs.

Josephson effect due to odd-frequency pairs in diffusive half metals
Yasuhiro Asano, Yukio Tanaka, Alexander A. Golubov
PHYSICAL REVIEW LETTERS, 98, 10, 107002.1-107002.4, AMER PHYSICAL SOC, 2007年03月
英語, 研究論文（学術雑誌）, Motivated by a recent experiment [Keizer et al., Nature (London) 439, 825 (2006)], we study the Josephson effect in superconductor/diffusive half metal/superconductor junctions using the recursive Green function method. The spin-flip scattering at the junction interfaces opens the Josephson channel of the odd-frequency spin-triplet Cooper pairs. As a consequence, the local density of states in a half metal has a large peak at the Fermi energy. Therefore the odd-frequency pairs can be detected experimentally by using the scanning tunneling spectroscopy.

Theory of tunneling spectroscopy in the Larkin-Ovchinnikov state
Yukio Tanaka, Yasuhiro Asano, Masanori Ichioka, Satoshi Kashiwaya
PHYSICAL REVIEW LETTERS, 98, 7, 077001.1-077001.4, AMER PHYSICAL SOC, 2007年02月
英語, 研究論文（学術雑誌）, We present a theory of tunneling spectroscopy for normal metal/Larkin-Ovchinnikov state junctions in which the spatial periodic modulation in the pair potential amplitude is taken into account. The tunneling spectra show the characteristic line shapes reflecting the minigap structures under the periodic pair potentials depending on the boundary condition of the pair potentials at the junction interface. These features are qualitatively different from the tunneling spectra of the Fulde-Ferrell state. We propose an experimental setup which identifies the superconducting state of CeCoIn5.

Anomalous Josephson current by odd frequency Cooper pairs
Yasuhiro Asano
Physica C: Superconductivity and its Applications, 460-462, 1327-1328, 2007年, ［査読有り］
英語, 研究論文（学術雑誌）

Josephson spin current in triplet superconductor junctions
Yasuhiro Asano
PHYSICAL REVIEW B, 74, 22, 220501, AMERICAN PHYSICAL SOC, 2006年12月
英語, 研究論文（学術雑誌）, This paper theoretically discusses the spin current in spin-triplet superconductor/insulator/spin-triplet superconductor junctions. At low temperatures, a midgap Andreev resonant state anomalously enhances not only the charge current but also the spin current. The coupling between the Cooper pairs and the electromagnetic fields leads to a Fraunhofer pattern in the direct current spin flow in magnetic fields and an alternative spin current under applied bias voltages.

Effect of the vortices on the nuclear spin relaxation rate in the unconventional pairing states of the organic superconductor (TMTSF)(2)PF6
M. Takigawa, M. Ichioka, K. Kuroki, Y. Asano, Y. Tanaka
PHYSICAL REVIEW LETTERS, 97, 18, 187002.1-187002.4, AMERICAN PHYSICAL SOC, 2006年11月
英語, 研究論文（学術雑誌）, This Letter theoretically discusses quasiparticle states and nuclear spin relaxation rates T-1(-1) in the quasi-one-dimensional superconductor (TMTSF)(2)PF6 under a magnetic field applied parallel to the conduction chains. We study the effects of Josephson-type vortices on T-1(-1) by solving the Bogoliubov-de Gennes equation for p-, d- or f-wave pairing interactions. In the presence of line nodes in pairing functions, T-1(-1) is proportional to T in sufficiently low temperatures because quasiparticles induced by vortices at the Fermi energy relax spins. We also try to identify the pairing symmetry of (TMTSF)(2)PF6.

Macroscopic quantum dynamics of pi junctions with ferromagnetic insulators
Shiro Kawabata, Satoshi Kashiwaya, Yasuhiro Asano, Yukio Tanaka, Alexander A. Golubov
PHYSICAL REVIEW B, 74, 18, AMER PHYSICAL SOC, 2006年11月, ［査読有り］
英語, 研究論文（学術雑誌）, We theoretically investigate the macroscopic quantum dynamics of a pi junction with a superconductor (S) and a multiferroic material or a ferromagnetic insulator (FI). By deriving the effective action from a microscopic Hamiltonian, a pi-junction qubit (a S-FI-S superconducting quantum interference device ring) is proposed. In this qubit, a quantum two-level system is spontaneously generated and the effect of the quasiparticle dissipation is found to be very weak. These features make it possible to realize a quiet qubit with high coherency. We also investigate macroscopic quantum tunneling (MQT) in current-biased S-FI-S pi junctions and show that the influence of the quasiparticle dissipation on MQT is negligibly small.

Josephson current through superconductor/diffusive-normal-metal/superconductor junctions: Interference effects governed by pairing symmetry
ASANO Yasuhiro, TANAKA Yukio, YOKOYAMA Takehito, KASHIWAYA Satoshi
Phys Rev B Condens Matter Mater Phys, 74, 6, 064507, 2006年08月
英語

Josephson current through superconductor/diffusive-normal-metal/superconductor junctions: Interference effects governed by pairing symmetry
Yasuhiro Asano, Yukio Tanaka, Takehito Yokoyama, Satoshi Kashiwaya
PHYSICAL REVIEW B, 74, 6, AMER PHYSICAL SOC, 2006年08月, ［査読有り］
英語, 研究論文（学術雑誌）, The Josephson effect in superconductor/diffusive-normal-metal/superconductor junctions is studied numerically by using the recursive Green function method. In superconductors, we consider spin-singlet s- and d-wave and spin-triplet p-wave pairing symmetries. The pairing symmetry governs two interference effects in junctions: the formation of a midgap Andreev resonant state at junction interfaces and the proximity effect in diffusive normal metals. A cooperative effect between the two interference effects causes anomalous Josephson current in a p-wave symmetry.

Nonmonotonic temperature dependence of critical current in diffusive d-wave junctions
T Yokoyama, Y Tanaka, AA Golubov, Y Asano
PHYSICAL REVIEW B, 73, 14, AMER PHYSICAL SOC, 2006年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the Josephson effect in D/I/DN/I/D junctions, where I, DN, and D denote an insulator, a diffusive normal metal, and a d-wave superconductor, respectively. The Josephson current is calculated based on the quasiclassical Green's function theory with a general boundary condition for unconventional superconducting junctions. In contrast to s-wave junctions, the product of the Josephson current and the normal-state resistance is enhanced by making the interface barriers stronger. The Josephson current has a nonmonotonic temperature dependence due to the competition between the proximity effect and the midgap Andreev resonant states.

Anomalous Josephson effect in p-wave dirty junctions
Y Asano, Y Tanaka, S Kashiwaya
PHYSICAL REVIEW LETTERS, 96, 9, 097007.1-097007.4, AMER PHYSICAL SOC, 2006年03月
英語, 研究論文（学術雑誌）, The Josephson effect in p-wave superconductor/diffusive normal metal/p-wave superconductor junctions is studied theoretically. Amplitudes of Josephson currents are several orders of magnitude larger than those in s-wave junctions. Current-phase (J-phi) relations in low temperatures are close to those in ballistic junctions such as J proportional to sin(phi/2) and J proportional to phi even in the presence of random impurity potentials. A cooperative effect between the midgap Andreev resonant states and the proximity effect causes such anomalous properties and is a character of the spin-triplet superconductor junctions.

Nonmonotonic temperature dependence of critical current in diffusive d -wave junctions
T. Yokoyama, Y. Tanaka, A. A. Golubov, Y. Asano
Physical Review B - Condensed Matter and Materials Physics, 73, 14, 140504, 2006年
英語, 研究論文（学術雑誌）, We study the Josephson effect in D/I/DN/I/D junctions, where I, DN, and D denote an insulator, a diffusive normal metal, and a d -wave superconductor, respectively. The Josephson current is calculated based on the quasiclassical Green's function theory with a general boundary condition for unconventional superconducting junctions. In contrast to s -wave junctions, the product of the Josephson current and the normal-state resistance is enhanced by making the interface barriers stronger. The Josephson current has a nonmonotonic temperature dependence due to the competition between the proximity effect and the midgap Andreev resonant states. © 2006 The American Physical Society.

Macroscopic quantum dynamics of π junctions with ferromagnetic insulators
Shiro Kawabata, Satoshi Kashiwaya, Yasuhiro Asano, Yukio Tanaka, Alexander A. Golubov
Physical Review B - Condensed Matter and Materials Physics, 74, 18, 180502, 2006年
英語, 研究論文（学術雑誌）, We theoretically investigate the macroscopic quantum dynamics of a π junction with a superconductor (S) and a multiferroic material or a ferromagnetic insulator (FI). By deriving the effective action from a microscopic Hamiltonian, a π -junction qubit (a S-FI-S superconducting quantum interference device ring) is proposed. In this qubit, a quantum two-level system is spontaneously generated and the effect of the quasiparticle dissipation is found to be very weak. These features make it possible to realize a quiet qubit with high coherency. We also investigate macroscopic quantum tunneling (MQT) in current-biased S-FI-S π junctions and show that the influence of the quasiparticle dissipation on MQT is negligibly small. © 2006 The American Physical Society.

Theory of thermal and charge transport in diffusive normal metal/superconductor junctions
T Yokoyama, Y Tanaka, AA Golubov, Y Asano
PHYSICAL REVIEW B, 72, 21, 214513, AMERICAN PHYSICAL SOC, 2005年12月
英語, 研究論文（学術雑誌）, Thermal and charge transport in diffusive normal metal (DN)/insulator/s-, d-, and p-wave superconductor junctions are studied based on the Usadel equation with the Nazarov's generalized boundary condition. We derive a general expression of the thermal conductance in unconventional superconducting junctions. Thermal conductance, electric conductance of junctions and their Lorentz ratio are calculated as a function of resistance in DN, the Thouless energy, magnetic scattering rate in DN and transparency of the insulating barrier. We also discuss transport properties for various orientation angles between the normal to the interface and the crystal axis of superconductors. It is demonstrated that the proximity effect does not influence the thermal conductance while the midgap Andreev resonant states suppress it. Dependencies of the electrical and thermal conductance on temperature are sensitive to pairing symmetries and orientation angles. The results imply a possibility to distinguish one pairing symmetry from another based on the results of experimental observations.

Anomalous features of the proximity effect in triplet superconductors
Y Tanaka, Y Asano, AA Golubov, S Kashiwaya
PHYSICAL REVIEW B, 72, 14, 140503.1-140503.4, AMERICAN PHYSICAL SOC, 2005年10月
英語, 研究論文（学術雑誌）, Anomalous features of the proximity effect specific to diffusive normal metal (DN) / triplet superconductor junctions are studied within the quasiclassical Green's function formalism. The pair amplitude f(N) as a function of energy epsilon in DN, satisfies an anomalous relation, f(N)(epsilon)=-f(N)(*)(-epsilon), contrary to that in singlet superconductor junctions case where f(N)(epsilon)=f(N)(*)(-epsilon). Such an unusual epsilon dependence is responsible for a zero energy peak in the local density of states and is a source of an anomalous penetration of the applied magnetic field into DN. Our results are relevant to Sr2RuO4, which is considered to have a p(x)+ip(y)-wave symmetry.

Spin current in p-wave superconducting rings
Y Asano
PHYSICAL REVIEW B, 72, 9, 092508.1-092508.4, AMERICAN PHYSICAL SOC, 2005年09月
英語, 研究論文（学術雑誌）, A formula of spin currents in mesoscopic superconductors is derived from the mean-field theory of superconductivity. Spin flow is generated by spatial gradient of d which represents a spin state of spin-triplet superconductors. We discuss a possibility of circulating spin currents in isolated p-wave superconducting rings at the zero magnetic field. The direction of spin currents depends on topological numbers which characterize spatial configurations of d on the ring.

Effect of zero-energy bound states on macroscopic quantum tunneling in high-T-c superconductor junctions
S Kawabata, S Kashiwaya, Y Asano, Y Tanaka
PHYSICAL REVIEW B, 72, 5, 052506.1-052506.4, AMERICAN PHYSICAL SOC, 2005年08月
英語, 研究論文（学術雑誌）, The macroscopic quantum tunneling (MQT) in the current biased high-T-c superconductor Josephson junctions and the effect of the zero-energy bound states (ZES) on the MQT are theoretically investigated. We obtained the analytical formula of the MQT rate and showed that the presence of the ZES at the normal/superconductor interface leads to a strong ohmic quasiparticle dissipation. Therefore the MQT rate is noticeably inhibited compared with the c-axis junctions in which the ZES are completely absent.

Josephson interferometer in a ring topology as a proof of the symmetry of Sr2RuO4
Y Asano, Y Tanaka, M Sigrist, S Kashiwaya
PHYSICAL REVIEW B, 71, 21, 214501.1-214501.7, AMERICAN PHYSICAL SOC, 2005年06月
英語, 研究論文（学術雑誌）, The Josephson effect is theoretically studied in two types of SQUIDs consisting of s wave superconductor and Sr2RuO4. Results show various response of the critical Josephson current to applied magnetic fields depending on the type of SQUID and on the pairing symmetries. In the case of a p(x)+ip(y) wave symmetry, the critical current in a corner SQUID becomes an asymmetric function of magnetic fields near the critical temperatures. Our results well explain a recent experimental finding [Nelson , Science 306, 1151 (2004)]. We also discuss effects of chiral domains on the critical current.

Influence of magnetic impurities on charge transport in diffusive-normal-metal/superconductor junctions
T. Yokoyama, Y. Tanaka, A. A. Golubov, J. Inoue, Y. Asano
Physical Review B - Condensed Matter and Materials Physics, 71, 9, 094506.1-094506.9, 2005年03月01日
英語, 研究論文（学術雑誌）, Charge transport in the diffusive normal metal (DN)/insulator/s- and d-wave superconductor junctions is studied in the presence of magnetic impurities in DN in the framework of the quasiclassical Usadel equations with the generalized boundary conditions. The cases of s- and d-wave superconducting electrodes are considered. The junction conductance is calculated as a function of a bias voltage for various parameters of the DN metal, resistivity, Thouless energy, the magnetic impurity scattering rate, and the transparency of the insulating barrier between DN and a superconductor. It is shown that the proximity effect is suppressed by magnetic impurity scattering in DN for any value of the barrier transparency. In low-transparent s-wave junctions this leads to the suppression of the normalized zero-bias conductance. In contrast to that, in high transparent junctions zero-bias conductance is enhanced by magnetic impurity scattering. The physical origin of this effect is discussed. For the d-wave junctions, the dependence on the misorientation angle a between the interface normal and the crystal axis of a superconductor is studied. The zero-bias conductance peak is suppressed by the magnetic impurity scattering only for low transparent junctions with α∼0. In other cases the conductance of the d-wave junctions does not depend on the magnetic impurity scattering due to strong suppression of the proximity effect by the midgap Andreev resonant states. ©2005 The American Physical Society.

Macroscopic quantum tunneling and quasiparticle dissipation in d-wave superconductor Josephson junctions
S Kawabata, S Kashiwaya, Y Asano, Y Tanaka
PHYSICAL REVIEW B, 70, 13, 132505.1-132505.4, AMERICAN PHYSICAL SOC, 2004年10月
英語, 研究論文（学術雑誌）, We examine the macroscopic quantum tunneling (MQT) in high-T-c superconductor Josephson junctions with a d-wave order parameter. Using a microscopic Hamiltonian and the functional integral method, we analytically obtain the MQT rate (the inverse lifetime of the metastable state) for the c-axis twist Josephson junctions. In the case of the zero twist angle, the system shows the super-Ohmic dissipation due to the presence of the nodal quasiparticle tunneling. Therefore, the MQT rate is strongly suppressed in comparison with the finite twist angle cases.

Macroscopic quantum tunneling and quasiparticle dissipation in d-wave superconductor Josephson junctions
S. Kawabata, S. Kashiwaya, Y. Asano, Y. Tanaka
Physical Review B - Condensed Matter and Materials Physics, 70, 13, 1, 132505, 2004年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We examine the macroscopic quantum tunneling (MQT) in high-Tc superconductor Josephson junctions with a d-wave order parameter. Using a microscopic Hamiltonian and the functional integral method, we analytically obtain the MQT rate (the inverse lifetime of the metastable state) for the c-axis twist Josephson junctions. In the case of the zero twist angle, the system shows the super-Ohmic dissipation due to the presence of the nodal quasiparticle tunneling. Therefore, the MQT rate is strongly suppressed in comparison with the finite twist angle cases.

Josephson effect in quasi one-dimensional unconventional superconductors
Y Asano, Y Tanaka, Y Tanuma, K Kuroki, H Tsuchiura
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73, 7, 1922, 1930, PHYSICAL SOC JAPAN, 2004年07月
英語, 研究論文（学術雑誌）, Josephson effect in junctions of quasi one-dimensional superconductors at the quarter-filling electron density is discussed by using the tight-binding model on a two-dimensional square lattice. To consider the triangular lattice structures in real materials such as (TMTSF)(2)X (X = PF6, ClO4, etc), the asymmetric hopping integral is introduced among second nearest lattice sites. A combination of these characters in superconductors (quasi one-dimensionality, quarter-filling electron density and weak triangular lattice structures) seriously affects the formation of a zero-energy state at a junction interface. As a consequence, calculated results of the Josephson current show anomalous dependences on temperatures.

Split of zero-bias conductance peak in normal-metal/d-wave superconductor junctions
Y Asano, Y Tanaka, S Kashiwaya
PHYSICAL REVIEW B, 69, 21, 214509.1-214509.12, AMER PHYSICAL SOC, 2004年06月
英語, 研究論文（学術雑誌）, Effects of impurity scatterings on the conductance in normal-metal/ d-wave superconductor junctions are discussed by using the single-site approximation. So far, the split of the zero-bias conductance peak has been believed to be evidence of the broken time reversal symmetry states at the surface of high- T-c superconductors. In this paper, however, it is shown that the impurity scattering near the interface also causes the split of the zero-bias conductance peak. Typical conductance spectra observed in experiments at finite temperatures and under external magnetic fields are explained well by the present theory.

Split of zero-bias conductance peak in normal-metal/d-wave superconductor junctions
Yasuhiro Asano, Yukio Tanaka, Satoshi Kashiwaya
Physical Review B - Condensed Matter and Materials Physics, 69, 21, 1, 214509, 2004年06月, ［査読有り］
英語, 研究論文（学術雑誌）, Effects of impurity scatterings on the conductance in normal-metal/d-wave superconductor junctions are discussed by using the single-site approximation. So far, the split of the zero-bias conductance peak has been believed to be evidence of the broken time reversal symmetry states at the surface of high-Tc superconductors. In this paper, however, it is shown that the impurity scattering near the interface also causes the split of the zero-bias conductance peak. Typical conductance spectra observed in experiments at finite temperatures and under external magnetic fields are explained well by the present theory.

Phenomenological theory of zero-energy Andreev resonant states
ASANO Y, TANAKA Y, KASHIWAYA S
Phys Rev B Condens Matter Mater Phys, 69, 13, 134501.1-134501.11, 2004年04月
英語

Phenomenological theory of zero-energy Andreev resonant states
Yasuhiro Asano, Yukio Tanaka, Satoshi Kashiwaya
Physical Review B - Condensed Matter and Materials Physics, 69, 13, 1, 134501, 2004年04月, ［査読有り］
英語, 研究論文（学術雑誌）, A conceptual consideration is given to a zero-energy state (ZES) at the surface of unconventional superconductors. The reflection coefficients in normal-metal/superconductor (NS) junctions are calculated based on a phenomenological description of the reflection processes of a quasiparticle. The phenomenological theory reveals the importance of the sign change in the pair potential for the formation of the ZES. The ZES is observed as the zero-bias conductance peak (ZBCP) in the differential conductance of NS junctions. The split of the ZBCP due to broken time-reversal symmetry states is naturally understood in the present theory. We also discuss effects of external magnetic fields on the ZBCP.

Phenomenological theory of zero-energy Andreev resonant states
Y Asano, Y Tanaka, S Kashiwaya
PHYSICAL REVIEW B, 69, 13, AMER PHYSICAL SOC, 2004年04月, ［査読有り］
英語, 研究論文（学術雑誌）, A conceptual consideration is given to a zero-energy state (ZES) at the surface of unconventional superconductors. The reflection coefficients in normal-metal/superconductor (NS) junctions are calculated based on a phenomenological description of the reflection processes of a quasiparticle. The phenomenological theory reveals the importance of the sign change in the pair potential for the formation of the ZES. The ZES is observed as the zero-bias conductance peak (ZBCP) in the differential conductance of NS junctions. The split of the ZBCP due to broken time-reversal symmetry states is naturally understood in the present theory. We also discuss effects of external magnetic fields on the ZBCP.

Magnetic levitation in liquid oxygen and its applications
Yasuhiro Asano
Physica C: Superconductivity and its Applications, 2004年
研究論文（学術雑誌）

Josephson effect in organic superconductors (TMTSF)2X　　　　　　　　　　　　　　　
Y. Asano, Y. Tanaka, K. Kuroki, Y. Tanuma, H. Tsuchiura, S. Kashiwaya
Journal of the Physical Society of Japan, 73, 7, 1922-1930, 2004年, ［査読有り］
英語, 研究論文（学術雑誌）

A theoretical study of tunneling conductance in PrOs4Sb12 superconducting junctions
Y Asano, Y Tanaka, Y Matsuda, S Kashiwaya
PHYSICAL REVIEW B, 68, 18, 184506.1-184506.8, AMER PHYSICAL SOC, 2003年11月
英語, 研究論文（学術雑誌）, The tunnel conductance in normal-metal/insulator/ProS(4)Sb(12) junctions is theoretically studied, where skutterudite ProS(4)Sb(12) is considered to be an unconventional superconductor. The conductance is calculated for several pair potentials which have been proposed in recent work. The results show that the conductance is sensitive to the relation between the direction of electric currents and the position of point nodes. The conductance spectra often deviate from the shape of bulk density of states. The sub gap spectra have peak structures in the case of the spin-triplet pair potentials. The results indicate that the tunnel conductance is a useful tool to obtain information of the pairing symmetry.

Josephson effect in d-wave superconductor junctions in a lattice model
S Shirai, H Tsuchiura, Y Asano, Y Tanaka, J Inoue, Y Tanuma, S Kashiwaya
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72, 9, 2299, 2307, PHYSICAL SOC JAPAN, 2003年09月
英語, Josephson current between two d-wave superconductors is calculated by using a lattice model. Here we consider two types of junctions, i.e., the parallel junction and the mirror-type junction. The maximum Josephson current (J(c)) shows a wide variety of temperature (T) dependence depending on the misorientation angles and the types of junctions. When the misorientation angles are not zero, the Josephson Current has anomalous temperature dependencies because of a zero energy state (ZES) at the interfaces. In the case of mirror-type junctions, J(c) has a non monotonic temperature dependence. These results are consistent with previous results based on the quasiclassical theory [Y. Tanaka and S. Kashiwaya: Phys. Rev. B 56 (1997) 892]. On the other hand, we find that the ZES disappears in several junctions because of the Friedel oscillations of the wave function, which is peculiar to the lattice model. In such junctions, the temperature dependence of J(c) is close to the Ambegaokar-Baratoff's relation.

Influence of impurity-scattering on tunneling conductance in d-wave superconductors with broken time reversal symmetry
N Kitaura, H Itoh, Y Asan, Y Tanaka, J Inoue, Y Tanuma, S Kashiwaya
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72, 7, 1718, 1723, PHYSICAL SOC JAPAN, 2003年07月
英語, 研究論文（学術雑誌）, Effects of impurity scattering on tunneling conductance in dirty normal-metal/insulator/superconductor junctions are studied based on the Kubo formula and the recursive Green function method. The zero-bias conductance peak (ZBCP) is a consequence of the unconventional pairing symmetry in superconductors. The impurity scattering in normal metals suppresses the amplitude of the ZBCP. The degree of the suppression agrees well with results of the quasiclassical Green function theory. When superconductors have d + is-wave pairing symmetry, the time-reversal symmetry is broken in superconductors and the ZBCP splits into two peaks. The random impurity scattering reduces the height of the two splitting peaks. The position of the splitting peaks, however, almost remains unchanged even in the presence of the strong impurity scattering. Thus the two splitting peaks never merge into a single ZBCP.

Josephson current in s-wave-superconductor/Sr2RuO4 junctions
Y Asano, Y Tanaka, M Sigrist, S Kashiwaya
PHYSICAL REVIEW B, 67, 18, 184505.1-184505.7, AMER PHYSICAL SOC, 2003年05月
英語, 研究論文（学術雑誌）, The Josephson current between an s-wave and a spin-triplet superconductor Sr2RuO4 (SRO) is studied theoretically. In spin-singlet/spin-triplet superconductor junctions, there is no Josephson current proportional to sin phi in the absence of the spin-flip scattering near junction interfaces, where phi is a phase difference across junctions. Thus, a dominant term of the Josephson current is proportional to sin 2phi. The spin-orbit scattering at the interfaces gives rise to the Josephson current proportional to cos phi, which is a direct consequence of the chiral paring symmetry in SRO.

Temperature dependence of spin-polarized transport in ferromagnet/unconventional superconductor junctions
T Hirai, Y Tanaka, N Yoshida, Y Asano, J Inoue, S Kashiwaya
PHYSICAL REVIEW B, 67, 17, 174501.1-174501.11, AMER PHYSICAL SOC, 2003年05月
英語, 研究論文（学術雑誌）, Tunneling conductance in ferromagnet/unconventional superconductor junctions is studied theoretically as a function of temperature and spin polarization in ferromagnets. In d-wave superconductor junctions, a zero-energy Andreev bound state drastically affects the temperature dependence of the zero-bias conductance (ZBC). In p-wave superconductor junctions, numerical results show various temperature dependences of the ZBC depending on the direction of the magnetic moment in ferromagnets and the pairing symmetry in superconductors such as p(x)-, p(y)-, and p(x)+ip(y)-wave symmetries. The last one is a candidate for the pairing symmetry of Sr2RuO4. From these characteristic features in the conductance, we may obtain information about the degree of spin polarization in ferromagnets and the direction of the d vector in spin-triplet superconductors.

Influence of the impurity-scattering on zero-bias conductance peak in ferromagnet/insulator/d-wave superconductor junctions
N Yoshida, Y Asano, H Itoh, Y Tanaka, J Inoue, S Kashiwaya
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72, 4, 895, 899, PHYSICAL SOC JAPAN, 2003年04月
英語, 研究論文（学術雑誌）, Effects of impurity-scattering on a zero-bias conductance peak in ferromagnet/insulator/d-wave superconductor junctions are theoretically studied. The impurities are introduced through the random potential in ferromagnets near the junction interface. As in the case of normal-metal/insulator/d-wave superconductor junctions, the magnitude of zero-bias conductance peak decreases with increasing the degree of disorder. However, when the magnitude of the exchange potential in ferromagnet is sufficiently large, the random potential can enhance the zero-bias conductance peak in ferromagnetic junctions.

Superconductivity in NCCO thin films and effect of Gd and Ni doping
Yasuhiro Asano
Physica C: Superconductivity and its Applications, 2003年
研究論文（学術雑誌）

Tunneling Spectra of Skutterudite PrOs4Sb12　　　　　　　　　　　　　　　
Y. Asano, Y. Tanaka, Y. Matsuda, S. Kashiwaya
Physical Review B, 68, 184506_1-8, 2003年, ［査読有り］
英語, 研究論文（学術雑誌）

Journal of Physical Society of Japan　　　　　　　　　　　　　　　
S. Shirai, H. Tsuchiura, Y. Asano, Y. Tanaka, J. Inoue, Y. Tanuma, S. Kashiwaya
Journal of Physical Society of Japan, 72, 9, 2299-2307, 2003年, ［査読有り］
英語, 研究論文（学術雑誌）

Josephson effect in junctions of Sr2RuO4
Y Asano, K Katabuchi
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71, 8, 1974, 1977, PHYSICAL SOC JAPAN, 2002年08月
英語, 研究論文（学術雑誌）, Josephson effect between two Sr2RuO4 (SRO) is theoretically studied based on a new formula of Josephson current. We analytically calculate the Josephson current in clean SRO/insulator/SRO junctions and SRO/dirty normal metal/SRO junctions. In SRO, we assume a spin-triplet p wave Superconductivity which breaks the chiral symmetry. When the current flows in a direction perpendicular to the c axis of SRO, the zero-energy states formed at the junction interfaces enhance the Josephson current in low temperature regime. We also report the Josephson current parallel to the c axis.

Unconventional superconductivity and Josephson effect in superconductor/dirty normal metal/superconductor junctions
Y Asano
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71, 3, 905, 909, PHYSICAL SOC JAPAN, 2002年03月
英語, 研究論文（学術雑誌）, A relation between amplitudes of Josephson current and nodes in excitation-gap of unconventional superconductors is studied in superconductor/dirty normal metal/superconductor junctions. It is found that ensemble average of the Josephson current vanishes when the junction interface is perpendicular to a plane which includes line- or point-zeros of the excitation-gap. A zero-energy state formed at the junction interface is a character of unconventional superconductor junctions and causes large sample-to-sample fluctuations in the Josephson current in low temperatures. The disappearance of the ensemble-averaged Josephson current and the large fluctuations occur at the same time when the Cooper pairs have d- or f-wave pairing symmetries.

Correlation between specular Andreev reflection and zero-energy states in normal-metal/d-wave-superconductor junctions　　　　　　　　　　　　　　　
Yasuhiro Asano, Yukio Tanaka
Physical Review B - Condensed Matter and Materials Physics, 65, 6, 645221, 645225, 2002年02月01日
英語, 研究論文（学術雑誌）, We report the effects of interfacial roughness on a zero-bias conductance peak (ZBCP) in normal-metal/d-wave-superconductor junctions. The roughness spoils to specularity of the junction interface, and causes a diffuse Andreev reflection of a quasiparticle. The ZBCP decreases linearly with a decreasing rate of the specular Andreev reflection at the interface. A sensitivity of the ZBCP to the roughness strongly depends on a transparency of the junctions. In low transparent junctions, the ZBCP disappears even in the regime of weak roughness. We also find a splitting of the ZBCP owing to the interfacial roughness in low transparent junctions.

Correlation between specular Andreev reflection and zero-energy states in normal-metal/d-wave-superconductor junctions
Y Asano, Y Tanaka
PHYSICAL REVIEW B, 65, 6, 064522.1-064522.5, AMERICAN PHYSICAL SOC, 2002年02月
英語, 研究論文（学術雑誌）, We report the effects of interfacial roughness on a zero-bias conductance peak (ZBCP) in normal-metal/d-wave-superconductor junctions. The roughness spoils to specularity of the junction interface, and causes a diffuse Andreev reflection of a quasiparticle. The ZBCP decreases linearly with a decreasing rate of the specular Andreev reflection at the interface. A sensitivity of the ZBCP to the roughness strongly depends on a transparency of the junctions. In low transparent junctions, the ZBCP disappears even in the regime of weak roughness. We also find a splitting of the ZBCP owing to the inter-facial roughness in low transparent junctions.

Josephson current through Anderson insulators
Yasuhiro Asano
Physical Review B - Condensed Matter and Materials Physics, 66, 17, 1, 6, 2002年
英語, 研究論文（学術雑誌）, The Josephson effect in superconductor / semiconductor / superconductor junctions is discussed, where semiconductors are in the localization-transport regime. The temperature dependence of the critical Josephson current (formula presented) in a single sample is very different from those in other samples. Thus it is impossible to predict the Josephson current in experiments from the ensemble average of the Josephson current in theories. A variety in the temperature-dependence of (formula presented) can be understood by an analysis of the normal conductance near the Fermi energy. In some samples, we find that (formula presented) first increases with decreasing temperatures then decreases in agreement with an recent experiment. © 2002 The American Physical Society.

Retro Property of a Quasiparticle and Zero energy States in Normal metal/ d-wave superconductor Junctions　　　　　　　　　　　　　　　
Y. Asano, Y. Tanaka
Physical Review B,, 65, 064522 _1-6, 2002年, ［査読有り］
英語, 研究論文（学術雑誌）

Direct-current Josephson effect in SNS junctions of anisotropic superconductors
Y Asano
PHYSICAL REVIEW B, 64, 22, 224515.1-224515.9, AMER PHYSICAL SOC, 2001年12月
英語, 研究論文（学術雑誌）, We derive a formula of the dc Josephson current between two superconductors with anisotropic pairing symmetry. One of the basic characters in the junctions of the anisotropic superconductors is the formation of the zero-energy bound states at the junction interfaces, which leads to the low-temperature anomaly of the Josephson current. The contribution of the zero-energy states to the Josephson current is taken into account in the present formalism.

Numerical method for dc Josephson current between d-wave superconductors
Y Asano
PHYSICAL REVIEW B, 63, 5, 052512.1-052512.4, AMER PHYSICAL SOC, 2001年02月
英語, 研究論文（学術雑誌）, We develop a numerical method to calculate the de Josephson current between the d(x2-y2)-wave superconductors. The Josephson junctions are described by the Bogoliubov-de Gennes equation on the two-dimensional tight-binding lattice. The Josephson current is expressed by the Matsubara Green function which is computed by the recursive Green-function method. We find in d-wave-superconductor/dirty-normal-metal/d-wave-superconductor junctions that the ensemble average of the Josephson current disappears for all temperature regimes when the angle between the crystal axis and the normal of the junction interface is pi /4.

Disappearance of ensemble-averaged Josephson current in dirty superconductor-normal-superconductor junctions of (formula presented)-wave superconductors
Yasuhiro Asano
Physical Review B - Condensed Matter and Materials Physics, 64, 1, 014511.1-014511.8, 2001年
英語, 研究論文（学術雑誌）, We discuss the Josephson current in superconductor/dirty normal conductor/superconductor junctions, where the superconductors have (formula presented) pairing symmetry. The low-temperature behavior of the Josephson current depends on the orientation angle between the crystalline axis and the normal of the junction interface. We show that the ensemble-averaged Josephson current vanishes when the orientation angle is (formula presented) and the normal conductor is in the diffusive transport regime. The (formula presented)-wave pairing symmetry is responsible for this fact. © 2001 The American Physical Society.

Effects of disorder on conductance oscillations in semiconductor-superconductor junctions in a magnetic field
Y Asano, T Yuito
PHYSICAL REVIEW B, 62, 11, 7477, 7482, AMER PHYSICAL SOC, 2000年09月
英語, 研究論文（学術雑誌）, We study the effects of disorder on magnetoconductance oscillations in semiconductor-superconductor junctions. These conductance oscillations were predicted by recent several theoretical works in ballistic junctions, however, have never been observed yet in experiments. We find that the disorder near the junction suppresses the conductance oscillations. From the numerical results, we derive a condition that must be satisfied to find the conductance oscillations in experiments.

Andreev reflection and cyclotron motion of a quasiparticle in high magnetic fields
Y Asano, T Kato
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 69, 4, 1125, 1135, PHYSICAL SOC JAPAN, 2000年04月
英語, 研究論文（学術雑誌）, We discuss the magnetoconductance oscillations in small junctions of a ballistic semiconductor and a superconductor. The conductance is calculated both numerically and analytically based on the Bogoliubov-de Gennes equation. The conductance oscillations appear when the Andreev reflection is not perfect at the interface and the diameter of the cyclotron motion of a quasiparticle is comparable to the width of the junction. An interplay between the cyclotron motion of a quasiparticle near the interface and the phase shift by the magnetic field is the origin of the conductance oscillations.

Magnetoconductance oscillations in ballistic semiconductor-superconductor junctions
Y Asano
PHYSICAL REVIEW B, 61, 3, 1732, 1735, AMER PHYSICAL SOC, 2000年01月
英語, 研究論文（学術雑誌）, The mechanism of the magnetoconductance oscillations in junctions of a ballistic semiconductor and a superconductor is discussed. The oscillations appear when both the normal and the Andreev refection occur at the interface. The interplay between the classical cyclotron motion of a quasiparticle and the phase shift caused by the magnetic field is the origin of the conductance oscillations.

Effects of in-plane magnetic fields on Coulomb oscillations of a double-quantum-dot molecule
Y Asano
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 67, 12, 4014, 4017, PHYSICAL SOC JAPAN, 1998年12月
英語, We studied the electronic structure and the electron transport in vertically coupled double quantum dots as a function of the number of electrons and strength of the magnetic field apl,lied in the direction perpendicular to the electric current. In weakly coupled double quantum dots, the electron correlation leads to the spin blockade in the Coulomb oscillations of the conductance. To date, however, it has been difficult to observe the spin blockade clearly since the temperature is not sufficiently low. We propose an experimental method to confirm the electron correlation effects even in the present temperature regime.

Electron-correlation effects in transport through a double-quantum-dot molecule
Y Asano
PHYSICAL REVIEW B, 58, 3, 1414, 1423, AMER PHYSICAL SOC, 1998年07月
英語, 研究論文（学術雑誌）, The effects of the electron correlation on the electronic structure and transport in a pair of vertically coupled quantum dots are studied as functions of the number of electrons and the distance between the two dots by using a numerical diagonalization method. The electron correlation drastically affects the spin structure of the ground states when the number of electrons and the distance between the dots are sufficiently large. The electronic states with the large (small) spin momentum are stable when the number of electrons is an odd (even) integer. A physical picture of this characteristic behavior can be understood by an analogy to that of the electronic states in the Hubbard model near half filling. The Coulomb oscillation can be seen in the conductance of the electric current through the double-quantum dots. When the distance between the dots is large, the amplitudes of several conductance peaks are suppressed by the electron correlation. [S0163-1829(98)00927-8].

Erratum: Conductance fluctuations near the ballistic-transport regime [Phys. Rev. B 54 , 11 602 (1996)]
Yasuhiro Asano
Physical Review B, 56, 15, 9972, 1997年10月15日, ［査読有り］
研究論文（学術雑誌）

Conductance fluctuations near the ballistic-transport regime
Yasuhiro Asano
Physical Review B, 54, 16, 11602, 11611, 1996年10月15日, ［査読有り］
研究論文（学術雑誌）

Conductance fluctuations near the ballistic-transport regime
Yasuhiro Asano, Gerrit E. W. Bauer
Physical Review B - Condensed Matter and Materials Physics, 54, 16, 11602, 11611, 1996年
英語, 研究論文（学術雑誌）, The fluctuations in the electric conduction of a short disordered region are studied theoretically. The ensemble-averaged conductance and its fluctuations are calculated analytically in the single-site approximation. For a small number of impurities, the mean square of the fluctuations increases in proportion to the number of impurities, but is independent of the system size
i.e., each impurity contributes independently to the fluctuations. Numerical simulations confirm the analytical results. The amplitude of the fluctuations can be larger than the universal values in diffusive conductors when the impurity scattering potential is sufficiently strong. In terms of random matrix theory, the enhancement can be understood by a reduced spectral rigidity of the transmission matrix eigenvalues. © 1996 The American Physical Society.

GIANT MAGNETORESISTANCE IN GRANULAR ALLOYS - 2-BAND MODEL
Y ASANO, A OGURI, J INOUE, S MAEKAWA
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 136, 1-2, L18, L22, ELSEVIER SCIENCE BV, 1994年09月
英語, Numerical simulation in the recursive Green's function method is extended to a two-band tight-binding model where itinerant s- and localized d-electrons coexist. This method enables us to make more realistic calculations of the giant magnetoresistance in magnetic multilayers and granular alloys containing noble metals, such as Co/Cu and Co/Ag. By using the present method, dependence of the magnetoresistance on the size of the magnetic clusters in granular alloys is examined and compared with the experimental one as well as with that calculated before in the single-band model.

Numerical study of the effect of Coulomb repulsion on resonant tunneling
Yasuhiro Asano
Physical Review B, 50, 4, 2667-2670, 1994年07月15日
英語, 研究論文（学術雑誌）

Giant magnetoresistance in magnetic granular alloys
Yasuhiro Asano
Physical Review B, 49, 18, 12831-12834, 1994年05月01日
英語, 研究論文（学術雑誌）

Parallel and perpendicular transport in multilayered structures
Yasuhiro Asano
Physical Review B, 48, 9, 6192-6198, 1993年09月01日
英語, 研究論文（学術雑誌）

EFFECTS OF INTERFACE ROUGHNESS ON CONDUCTANCE IN SUPERLATTICES
A OGURI, Y ASANO, S MAEKAWA
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 61, 8, 2652, 2655, PHYSICAL SOCIETY JAPAN, 1992年08月
英語, The conductance in superlattices is studied using the Landauer formula with a transfer-matrix technique. The characteristics of the superlattice, i.e., the layer structure and roughness at interfaces, are treated in a tight-binding model on a two-dimensional long-strip lattice. In this context the magnetoresistance of a magnetic Fe/Cr superlattice, which is known to show giant magnetoresistance, is discussed.

磁気クラスター下での対ポテンシャルのπ位相シフト
SUZUKI Shu-Ichiro, SATO Takumi, ASANO Yasuhiro, JPS Conference Proceedings (Web), 38, 2023年

ボゴリューボフ・フェルミ面上の準粒子と奇周波数クーパー対
KIM Dakyeong, 小林伸吾, 浅野泰寛, 日本物理学会講演概要集(CD-ROM), 77, 1, 2022年

弱い磁化を伴うメソスコピック超伝導接合における準粒子スペクトル
SUZUKI S.-I., GOLUBOV A. A., GOLUBOV A. A., ASANO Y., ASANO Y., TANAKA Y., JPS Conference Proceedings (Web), 30, 2020年

ナノスケールCa₂RuO₄単結晶におけるBKT転移の観測
小笠原優仁, 柳原興世, 延兼啓純, 國貞雄治, 野村一成, 能村貴宏, 秋山友寛, 秋山友寛, 浅野泰寛, 丹田聡, 日本物理学会講演概要集(CD-ROM), 73, 1, ROMBUNNO.22aK503‐11, 1903, 2018年03月23日
一般社団法人 日本物理学会, 日本語

ルテニウム酸化物における超伝導-絶縁体転移と臨界指数
延兼啓純, 柳原興世, 國貞雄治, 小笠原優仁, 礒野翔, 野村一成, 能村貴宏, 秋山友宏, 秋山友宏, 浅野泰寛, 丹田聡, 日本物理学会講演概要集(CD-ROM), 73, 2, 2018年

2次元Ca₂RuO₄における高温超伝導
延兼啓純, 柳原興世, 國貞雄治, 小笠原優仁, 野村一成, 能村貴宏, 秋山友宏, 秋山友宏, 浅野泰寛, 丹田聡, 日本物理学会講演概要集(CD-ROM), 72, 2, ROMBUNNO.24aF11‐2, 2054, 2017年09月25日
一般社団法人 日本物理学会, 日本語

Josephson effect in a multiorbital model for Sr2RuO4 (vol 95, 174518, 2017)
Kohei Kawai, Keiji Yada, Yukio Tanaka, Yasuhiro Asano, Alexander A. Golubov, Satoshi Kashiwaya, PHYSICAL REVIEW B, 95, 21, 2017年06月
AMER PHYSICAL SOC, 英語, その他

Observation of localized high-$T_c$ superconductivity in a Ca$_2$RuO$_4$ nanofilm single crystal
Hiroyoshi Nobukane, Kosei Yanagihara, Yuji Kunisada, Yunito Ogasawara, Kazushige Nomura, Yasuhiro Asano, Satoshi Tanda, 2017年03月28日
We report two-dimensional superconducting phase fluctuations in a

Ca$_2$RuO$_4$ nanofilm single crystal. A thin film of Ca$_2$RuO$_4$ exhibits

typical Kosterlitz-Thouless transition behaviour around $T_{\mathrm{KT } }=30$ K.

We also found that the bias current applied to the thin film causes a

superconducotor-insulator transition at low temperatures. The film is

superconductive for small bias currents and insulating for large bias currents.

The two phases are well separated by the critical sheet resistance of the thin

film 16.5 k$\Omega$. In addition to these findings, our results suggest the

presence of superconducting fluctuations at a high temperature $T=96$ K with

onset. The fabrication of nanofilms made of layered material enables us to

discuss rich superconducting phenomena in ruthenates., 機関テクニカルレポート，技術報告書，プレプリント等

多重縮退したトポロジカル表面状態の安定性と指数定理 II
池谷聡, 小林伸吾, 浅野泰寛, 日本物理学会講演概要集(CD-ROM), 72, 2, 2017年

10aBB-10 ドレッセルハウス型スピン軌道相互作用のある超伝導ナノワイヤーにおける輸送現象(10aBB 超伝導,領域6(金属(液体金属・準結晶)・低温(超低温・超伝導・密度波)))
池谷 聡, 浅野 泰寛, 日本物理学会講演概要集, 69, 2, 583, 583, 2014年08月22日
一般社団法人日本物理学会, 日本語

7pBA-8 Properties of Odd-frequency pairs(7pBA Division 6・4・8 Joint Symposium Odd-frequency pairing -current status-)
Asano Yasuhiro, 日本物理学会講演概要集, 69, 2, 560, 560, 2014年08月22日
一般社団法人日本物理学会, 英語

7aBB-6 微小な超伝導体が示す異常な磁気応答に於ける不純物効果(7aBB 超伝導・密度波,領域6(金属(液体金属・準結晶)・低温(超低温・超伝導・密度波)))
鈴木 修, 浅野 泰寛, 日本物理学会講演概要集, 69, 2, 555, 555, 2014年08月22日
一般社団法人日本物理学会, 日本語

29pAW-3 3次元系における対称性の破れたトポロジカル状態(29pAW トポロジカル絶縁体・超伝導体(理論),領域4(半導体,メゾスコピック系・局在))
羽部 哲朗, 浅野 泰寛, 日本物理学会講演概要集, 69, 1, 719, 719, 2014年03月05日
一般社団法人日本物理学会, 日本語

30aCA-7 微小な異方的超伝導体の磁気応答2(30aCA 超伝導・密度波,領域6(金属(液体金属・準結晶)・低温(超低温・超伝導・密度波)))
鈴木 修, 浅野 泰寛, 日本物理学会講演概要集, 69, 1, 812, 812, 2014年03月05日
一般社団法人日本物理学会, 日本語

27aDK-6 2つの異なるトポロジカル絶縁体の接合界面に生じる2次元電子状態の安定性(トポロジカル絶縁体・超伝導体,領域4,領域7合同,領域4(半導体,メゾスコピック系・局在))
羽部 哲朗, 浅野 泰寛, 日本物理学会講演概要集, 68, 2, 628, 628, 2013年08月26日
一般社団法人日本物理学会, 日本語

26aDC-1 メゾスコピックな異方的超伝導体の磁気応答(超伝導,領域6(金属,超低温,超伝導・密度波))
鈴木 修, 浅野 泰寛, 日本物理学会講演概要集, 68, 2, 713, 713, 2013年08月26日
一般社団法人日本物理学会, 日本語

29aRG-10 マヨラナフェルミオンと奇周波数クーパー対(29aRG 超伝導・密度波,領域6(金属,超低温,超伝導・密度波))
浅野 泰寛, 田仲 由喜, 日本物理学会講演概要集, 68, 1, 894, 894, 2013年03月26日
一般社団法人日本物理学会, 日本語

29aRG-7 強磁性体/超伝導体接合における奇周波数ペアリングとスピンsinglet-tripletクロスオーバー(29aRG 超伝導・密度波,領域6(金属,超低温,超伝導・密度波))
川畑 史郎, 浅野 泰寛, 田仲 由喜夫, Golubov A. A., 日本物理学会講演概要集, 68, 0, 894, 894, 2013年
一般社団法人 日本物理学会, 英語

超伝導による量子もつれ光子対源の可能性とその展望
末宗幾夫, 笹倉弘理, 浅野泰寛, 熊野英和, 応用物理, 81, 12, 1029-1033, 1033, 2012年12月10日
応用物理学会, 日本語

トポロジカル絶縁体/強磁性体における新たな2次元電子状態の理論
羽部哲朗, 浅野泰寛, 日本物理学会講演概要集, 67, 2, 630, 630, 2012年08月24日
一般社団法人日本物理学会, 日本語

Spin Josephson effect with a single superconductor (vol 83, 180504, 2011)
P. M. R. Brydon, Yasuhiro Asano, Carsten Timm, PHYSICAL REVIEW B, 85, 13, 2012年04月
AMER PHYSICAL SOC, 英語, その他

25pBC-1 奇周波数クーパー対の物理 : はじめに(25pBC 領域6,領域8合同シンポジウム主題:奇周波数クーパー対の物理,領域6(金属,超低温,超伝導・密度波))
浅野 泰寛, 日本物理学会講演概要集, 67, 1, 839, 839, 2012年03月05日
一般社団法人日本物理学会, 日本語

空間反転対称性のない超伝導体におけるジョセフソン効果の低温異常
浅野泰寛, 山野聡, 日本物理学会講演概要集, 67, 1, 838, 838, 2012年03月05日
一般社団法人日本物理学会, 日本語

Photon-pair generation based on superconductivity
Ikuo Suemune, Hirotaka Sasakura, Yasuhiro Asano, Hidekazu Kumano, Ryotaro Inoue, Kazunori Tanaka, Tatsushi Akazaki, Hideaki Takayanagi, IEICE ELECTRONICS EXPRESS, 9, 14, 1184, 1200, 2012年
Superconductivity and optoelectronics have developed almost independently and had very rare interactions with each other in science and technologies. However recent interdisciplinary research opens up the potential for developing new optoelectronic devices. This review paper presents our recent theoretical and experimental demonstrations that superconductivity significantly modifies and accelerates photon generation processes. We have prepared superconducting light emitting diodes (LEDs) emitting at similar to 1.6-mu m optical-fiber communication band for the experimental demonstrations. This new-type LED operation is based on a unique physics related to Cooper-pair interband transition in a semiconductor, and further research leads to the solid-state simultaneously generated photon-pair sources for the potential application in quantum information and communication., IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, 英語, 書評論文,書評,文献紹介等

奇周波数クーパー対が示す異常な表面インピーダンス
浅野泰寛, GOLUBOV A. A, FOMINOV Ya. V, 田仲由喜夫, 日本物理学会講演概要集, 66, 2, 812, 812, 2011年08月24日
一般社団法人日本物理学会, 日本語

26aEG-11 奇周波数クーパー対が示す異常な表面インピーダンス(26aEG 超伝導,領域6(金属,超低温,超伝導・密度波))
浅野 泰寛, Golubov A. A., Fominov Ya. V., 田仲 由喜夫, 日本物理学会講演概要集, 66, 1, 818, 818, 2011年03月03日
一般社団法人日本物理学会, 日本語

Odd-frequency pairing in superconducting heterostructures
A. A. Golubov, Y. Tanaka, Y. Asano, Y. Tanuma, NanoScience and Technology, 56, 117, 131, 2011年
We review the theory of odd-frequency pairing in superconducting hetero structures, where an odd-frequency pairing component is induced near interfaces. General description of superconducting proximity effect in a normal metal or a ferromagnet attached to an unconventional superconductor (S) is given within quasi classical kinetic theory for various types of symmetry state in S. Various possible symmetry classes in a superconductor are considered, which are consistent with the Paula principle: even-frequency spin-singlet even-parity (ESE) state, even frequency spin-triplet odd-parity (ETO) state, odd-frequency spin-triplet even-parity (OTE) state and odd-frequency spin-singlet odd-parity (OSO) state. As an example, we consider junction between a diffusive normal metal (DN) and a p-wave superconductor (even-frequency spin-triplet odd-parity symmetry), where the pairing amplitude in DN belongs to an odd-frequency spin-triplet even-parity symmetry class. We also discuss the manifestation of odd-frequency pairing in conventional superconductor/normal (S/N) proximity systems and its relation to the classical McMillan-Rowell oscillations. © Springer-Verlag Berlin Heidelberg 2011., 英語, 書評論文,書評,文献紹介等

Exploring Spontaneous Simultaneous Photon-pair Generation in Semiconductors
I. Suemune, Y. Asano, K. Tanaka, R. Inoue, H. Takayanagi, H. Sasakura, T. Akazaki, H. Kumano, PHYSICS OF SEMICONDUCTORS: 30TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, 1399, 411-412, 2011年
Potential of generating entangled photon pairs from a Cooper-pair light emitting diode is demonstrated with experimental and theoretical studies., AMER INST PHYSICS, 英語

異方的超伝導とその近接効果
浅野泰寛, 田仲由喜夫, 物性研究, 95, 2, 113-151, 2010年11月05日
日本語

異方的超伝導とその近接効果(<シリーズ>超伝導・超流動研究の接点)
浅野 泰寛, 田仲 由喜夫, 物性研究, 95, 2, 113, 151, 2010年11月05日
物性研究刊行会, 日本語

マヨラナエッジ状態を介したヘリカル超伝導体のトンネル現象
浅野泰寛, 田仲由喜夫, 永長直人, 日本物理学会講演概要集, 65, 2, 742, 742, 2010年08月18日
一般社団法人日本物理学会, 日本語

スピン3重項超伝導体/強磁性体接合におけるスピン流
浅野泰寛, BRYDON Philip M.R, 日本物理学会講演概要集, 65, 1, 827, 827, 2010年03月01日
一般社団法人日本物理学会, 日本語

Theory of Josephson transport through spintronics nano-structures
Shiro Kawabata, Yasuhiro Asano, Yukio Tanaka, Satoshi Kashiwaya, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 42, 4, 1010, 1013, 2010年02月
We study the Josephson transport through ferromagnetic insulators (FIs) by taking into account its band structure explicitly. In the case of the fully polarized FIs (FPFIs), we found the formation of a pi-junction and an atomic-scale 0-pi transition induced by increasing the FI thickness. More remarkably, in the Josephson junction through spin-filter materials such as Eu chalcogenides, the orbital hybridization between the conduction d and the localized f electron gives rise to the pi-junction behavior. Such FI-based pi-junctions can be used to implement highly coherent solid-state quantum bits. (C) 2009 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Josephson transport through a ferromagnet/superconductor hybrid structure and its application to quantum bit
KAWABATA Shiro, KAWABATA Shiro, ASANO Yasuhiro, Proc 2010 Int Symp Phys Quantum Technol, 160, 2010年
英語

Transport Properties in a Single Domain of Microscale Sr2RuO4 Single Crystals
Hiroyoshi Nobukane, Katsuhiko Inagaki, Satoshi Tsuchiya, Yasuhiro Asano, Koichi Ichimura, Kazuhiko Yamaya, Shigeru Takayanagi, Ikuto Kawasaki, Kenichi Tenya, Hiroshi Amitsuka, Satoshi Tanda, JAPANESE JOURNAL OF APPLIED PHYSICS, 49, 2, 020209.1-020209.3, 2010年
We report our approach to measuring the transport properties in a single chiral order parameter domain of microscale Sr2RuO4 single crystals. Sr2RuO4 single crystals were grown by the solid-phase reaction. Microscale single crystals were deposited from a dispersed liquid, and selected from the result of the chemical composition and crystallinity of the dispersed crystals. The selected crystals attached to gold electrodes show superconducting properties. We also found the anomalous current-voltage characteristics that show that induced voltage is an even function of bias current. (C) 2010 The Japan Society of Applied Physics, JAPAN SOC APPLIED PHYSICS, 英語

20aHW-3 強磁性絶縁体/超伝導体ジョセフソン接合におけるπ接合の理論(20aHW 微小接合,領域4(半導体,メゾスコピック系・局在))
川畑 史郎, 浅野 泰寛, 田仲 由喜夫, 柏谷 聡, Golubov A. A., 日本物理学会講演概要集, 65, 0, 700, 700, 2010年
一般社団法人 日本物理学会, 日本語

Sr₂RuO₄のマイクロデバイスの輸送特性
柏谷聡, 神原浩, 柏谷裕美, 松本哲朗, 古田剛, 矢口宏, 浅野泰寛, 田仲由喜夫, 前野悦輝, 日本物理学会講演概要集, 64, 2, 690, 690, 2009年08月18日
一般社団法人日本物理学会, 日本語

拡散的常伝導体/超伝導体接合系におけるスピン揺らぎの効果
重田出, 横山毅人, 浅野泰寛, 廣井政彦, 田仲由喜夫, 日本物理学会講演概要集, 64, 2, 482, 482, 2009年08月18日
一般社団法人日本物理学会, 日本語

Sr₂RuO₄‐Ru共晶系における磁場中局所伝導測定
神原浩, 柏谷聡, 矢口宏, 浅野泰寛, 田仲由喜夫, 前野悦輝, 日本物理学会講演概要集, 64, 2, 409, 409, 2009年08月18日
一般社団法人日本物理学会, 日本語

単一ドメインSr₂RuO₄におけるパリティ破れの発見
延兼啓純, 稲垣克彦, 市村晃一, 山谷和彦, 高柳滋, 川崎郁斗, 天谷健一, 網塚浩, 金野幸吉, 浅野泰寛, 本間龍也, 丹田聡, 日本物理学会講演概要集, 64, 2, 410, 410, 2009年08月18日
一般社団法人日本物理学会, 日本語

Effect of d-f hybridization on the Josephson current through Eu-chalcogenides
S. Kawabata, Y. Asano, Y. Tanaka, S. Kashiwaya, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 15-20, 1621, 1623, 2009年08月
A superconducting ring with a pi junction made from superconductor/ferroniagnetic-metal/superconductor (S-FM-S) exhibits a spontaneous current without an external magnetic field in the ground state. Such pi ring provides so-called quiet qubit that can be efficiently decoupled from the fluctuation of the external field. However, the usage of the FM gives rise to strong Ohmic dissipation. Therefore, the realization of pi junctions without FM is expected for qubit applications. We theoretically consider the possibility of the pi coupling for S/Eu-chalcogenides/S junctions based on the d-f Hamiltonian. By use of the Green's function method we found that pi junction can be formed in the case of the finite d-f hybridization between the conduction d and the localized f electrons. (C) 2009 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Chiral superconducting phase transition in 3-K phase of Sr2RuO4
H. Kambara, S. Kashiwaya, H. Yaguchi, Y. Asano, Y. Tanaka, Y. Maeno, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 15-20, 1030, 1033, 2009年08月
We have investigated the transports of micro-fabricated sample of 3-K phase superconductivity (T-c similar to 3 K) in Sr2RuO4-Ru eutectic system in order to clarify the pairing symmetry. Up to now, pure Sr2RuO4 (T-c = 1.5 K: 1.5-K phase) is widely recognized to be a spin-triplet odd-parity superconductor. However, the enhancement mechanism of T-c up to 3 K and the pairing symmetry of the 3-K phase have not been cleared yet. By using micro fabrication technique with focused ion beam, we have succeeded to extract individual superconducting channels for the 3-K phase in which only a few pieces of Ru inclusions are contained. Multiple kink structures observed in differential resistance-current (dV/dI - I) characteristics indicate serially connected superconducting filaments in the 3-K phase. We confirm that the 3-K phase is an odd-parity superconductor similar to pure Sr2RuO4 from the monotonous temperature dependence of the critical currents. In addition, we observed a quite unusual hysteresis in dV/dI - I below 2 K, which Suggests the internal degrees of freedom in the superconducting state: the most probably the chiral p-wave state. (C) 2009 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

宇宙における渦状構造とチャーン・サイモン重力理論 (オイラー方程式の数理 : 渦運動150年)
金野 幸吉, 松山 豊樹, 浅野 泰寛, 丹田 聡, 数理解析研究所講究録, 1642, 0, 164, 173, 2009年04月
京都大学, 日本語

Sr₂RuO₄‐Ru共晶系における3‐K相超伝導の伝導特性 II
神原浩, 柏谷聡, 矢口宏, 浅野泰寛, 田仲由喜夫, 前野悦輝, 日本物理学会講演概要集, 64, 1, 637, 637, 2009年03月03日
一般社団法人日本物理学会, 日本語

超伝導体/希薄磁性半導体接合の輸送特性
赤崎達志, 澤雄生, 横山毅人, 田仲由喜夫, GOLUBOV Alexander, 浅野泰寛, 柳暁志, 宗片比呂夫, 高柳英明, 高柳英明, 物性研究, 91, 3, 248, 2008年12月20日
日本語

超伝導体/強磁性体接合の最近の話題
浅野泰寛, 物性研究, 91, 3, 246, 2008年12月20日
日本語

超伝導体/強磁性体接合の最近の話題(不均一超伝導超流動状態と量子物理,研究会報告)
浅野 泰寛, 物性研究, 91, 3, 246, 246, 2008年12月20日
この論文は国立情報学研究所の電子図書館事業により電子化されました。, 物性研究刊行会, 日本語

Sr₂RuO₄‐Ru共晶系における3‐K相超伝導の伝導特性
神原浩, 柏谷聡, 矢口宏, 浅野泰寛, 田仲由喜夫, 前野悦輝, 日本物理学会講演概要集, 63, 2, 567, 567, 2008年08月25日
一般社団法人日本物理学会, 日本語

クーパーペアの形と近接効果
田仲由喜夫, 田仲由喜夫, 浅野泰寛, GOLUBOV Alexander, 日本物理学会講演概要集, 63, 2, 698, 698, 2008年08月25日
一般社団法人日本物理学会, 日本語

グラフェン上の強磁性/超伝導接合におけるアンドレーエフ反射
浅野泰寛, 吉田敏寛, 田中由喜夫, GOLUBOV A. A, 日本物理学会講演概要集, 63, 2, 769, 769, 2008年08月25日
一般社団法人日本物理学会, 日本語

Quasiparticle density of states in a half metal in the presence of odd-frequency Cooper pairs
Yasuhiro Asano, Takehito Yokoyama, Yukio Tanaka, Alexander A. Golubov, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 205, 5, 1023, 1025, 2008年05月
We study the local density of states in a half metal sandwiched by the two superconductors. The spin-flip scattering at the junction interface opens the Josephson channels of the odd-frequency spin-triplet s-wave Cooper pairs. The penetration of the odd-frequency pairs enhances the quasiparticle density of states near the Fermi energy in a half metal, which is responsible for the unusual nonmonotonic temperature dependence of the Josephson current. On the basis of calculated results, we propose experiments to confirm the odd-frequency Cooper pairs., WILEY-V C H VERLAG GMBH, 英語

23pQB-4 Odd-frequency pairing state in superconductor/ferromagnet junctions(Recent activities in physics of ferromagnet / superconductor junctions)
Asano Yasuhiro, 日本物理学会講演概要集, 63, 1, 458, 458, 2008年02月29日
一般社団法人日本物理学会, 英語

Odd-frequency pairing state in superconductor/ferromagnet junctions
ASANO Y, 日本物理学会講演概要集, 63, 1, 458, 2008年02月29日
英語

コンダクタンス分光による超伝導対称性の峻別
浅野泰寛, 田中由喜夫, GOLUBOV A. A, 柏谷聡, 日本物理学会講演概要集, 63, 1, 559, 559, 2008年02月29日
一般社団法人日本物理学会, 日本語

Bi‐2212積層型トンネル接合のアンドレエーフ共鳴状態におけるペアポテンシャルの空間変化を考慮した解析
重田出, 田辺慶忠, 浅野泰寛, 廣井政彦, 田仲由喜夫, 日本物理学会講演概要集, 63, 1, 559, 559, 2008年02月29日
一般社団法人日本物理学会, 日本語

Sr₂RuO₄における奇周波数超伝導対状態の探索
神原浩, 柏谷聡, 矢口宏, 浅野泰寛, 田仲由喜夫, 前野悦輝, 日本物理学会講演概要集, 63, 1, 560, 560, 2008年02月29日
一般社団法人日本物理学会, 日本語

領域6,領域8「不均一超伝導・超流動の物理」(第62回年次大会シンポジウムの報告)
浅野 泰寛, 日本物理學會誌, 63, 2, 137, 137, 2008年02月05日
一般社団法人日本物理学会, 日本語

THRESHOLD TEMPERATURE OF ZERO-BIAS CONDUCTANCE PEAK AND ZERO-BIAS CONDUCTANCE DIP IN DIFFUSIVE NORMAL METAL SUPERCONDUCTOR JUNCTIONS
Yasuhiro Asano, Controllable Quantum States: Mesoscopic Superconductivity and Sprintronics, 111, 117, 2008年01月01日
We have studied how zero-bias conductance dip (ZBCD) and zero-bias conductance peak (ZBCP) are smeared by increasing temperature in the diffusive normal metal (DN) / s-wave or d-wave superconductor junctions using the theory based on the Keldysh-Nambu quasiclassical Green's function formalism. Tunneling conductance is calculated by changing the magnitudes of the resistance in DN, the Thouless energy in DN, the transparency of the insulating barrier, and the angle between the normal to the interface and the crystal axis of d-wave superconductors. We present a threshold temperature from a possible observation of the ZBCD and ZBCP in line shapes of tunneling conductance.

22pYF-2 スピンフィルター効果を用いてπ接合を実現できるか?(22pYF 微小接合,領域4(半導体,メゾスコピック系・局在))
川畑 史郎, 浅野 泰寛, 田仲 由喜夫, 柏谷 聡, 日本物理学会講演概要集, 63, 0, 613, 613, 2008年
一般社団法人 日本物理学会, 日本語

Andreev bound states in dirty unconventional superconductor junctions
S. Kashiwaya, T. Matsumoto, H. Kashiwaya, H. Yaguchi, Y. Maeno, Y. Tanaka, Y. Asano, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 463, 14, 18, 2007年10月
We review the recent development in the theory of proximity effect in unconventional superconductor junctions. The low energy transport in the unconventional superconductor junction is governed by two interference effects of a quasiparticle: formation of a midgap Andreev resonant state (MARS) at the junction interface and the diffusion of Cooper pair into a normal-metal (proximity effect). Both of them are sensitive to the pairing symmetry of superconductivity. In a p-wave superconductor junction, the MARS penetrates from a superconductor into a normal-metal and drastically increases the conductance and the Josephson current. We will show that such anomalous quantum transport is the result of a cooperative effect between the MARS and the proximity effect. Experimental trials to detect the Josephson current between two p-wave superconductors are in progress. (C) 2007 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Josephson current through a diffusive half metal
Y. Asano, Y. Tanaka, A. A. Golubov, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 463, 19, 22, 2007年10月
This paper discusses the Josephson effect in superconductor/diffusive half metal/superconductor junctions. The spin-flip scattering at the junction interfaces opens a Josephson channel between the two spin-singlet superconductors. The odd-frequency equal-spin-triplet Cooper pairs carry the Josephson current. As a consequence, the local density of states in a half metal has a large peak at the Fermi energy. We propose an experimental method to detect odd-frequency pairs by using the scanning tunneling spectroscopy. (C) 2007 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Temperature dependence of tunneling conductance in diffusive normal metal/triplet superconductor junctions
Yasuhiro Asano, Physica C: Superconductivity and its Applications, 460, 1319, 1320, 2007年09月01日
The thermal broadening effect on the tunneling conductance in diffusive normal metal/triplet superconductor (DN/TS) junctions is studied based on the Usadel equation under the generalized boundary condition. The zero-bias conductance peak (ZBCP) enhances in the antinodal direction, due to the coexistence of the proximity effect and the midgap Andreev resonant states at the DN/TS junction interface. It is found that the ZBCP is affected by the thermal broadening effect especially for tunnel junctions with the low transparency and the small Thouless energy. © 2007 Elsevier B.V. All rights reserved.

22pWJ-1 「不均一超流動・超伝導の物理」はじめに(領域6,領域8合同シンポジウム,主題 : 不均一超流動・超伝導の物理,領域8,強相関係:高温超伝導,強相関f電子系など)
浅野 泰寛, 日本物理学会講演概要集, 62, 2, 610, 610, 2007年08月21日
一般社団法人日本物理学会, 日本語

Bi‐2212積層型接合のトンネルスペクトルにおけるペアポテンシャルの空間変化を考慮した解析
重田出, 田沼慶忠, 浅野泰寛, 廣井政彦, 田仲由喜夫, 日本物理学会講演概要集, 62, 2, 529, 529, 2007年08月21日
一般社団法人日本物理学会, 日本語

カイラルp波超伝導でのリトル・パークス振動
市岡優典, 町田一成, 石棉元, 瀧川光明, 瀧川光明, 浅野泰寛, 日本物理学会講演概要集, 62, 2, 587, 587, 2007年08月21日
一般社団法人日本物理学会, 日本語

奇周波数クーパー対と超伝導近接効果
田仲由喜夫, 浅野泰寛, 横山毅人, 固体物理, 42, 6, 345-363, 363, 2007年06月15日
アグネ技術センタ-, 日本語

19pZC-5 ハーフメタルを用いジョセフソンπ接合(9pZC 領域3,領域4合同招待講演,微小領域磁性,領域3(磁性,磁気共鳴))
浅野 泰寛, 澤 雄生, 田仲 由喜夫, 日本物理学会講演概要集, 62, 1, 463, 463, 2007年02月28日
一般社団法人日本物理学会, 日本語

19aPS-19 拡散的常伝導体/トリプレット超伝導体接合系のコンダクタンスの温度依存性(19aPS 領域8ポスターセッション(低温),領域8(強相関系:高温超伝導,強相関f電子系など))
重田 出, 横山 毅人, 浅野 泰寛, 田仲 由喜夫, 日本物理学会講演概要集, 62, 1, 560, 560, 2007年02月28日
一般社団法人日本物理学会, 日本語

20aXE-7 FFLO状態におけるトンネル効果の理論(20aXE 接合系磁束系など(理論),領域8(強相関系:高温超伝導,強相関f電子系など))
田仲 由喜夫, 浅野 泰寛, 市岡 優典, 柏谷 聡, 日本物理学会講演概要集, 62, 1, 616, 616, 2007年02月28日
一般社団法人日本物理学会, 日本語

18aRC-3 SIS接合におけるジョセフソンスピン流(微小接合,領域4,半導体,メゾスコピック系・局在)
浅野 泰寛, 日本物理学会講演概要集, 62, 1, 653, 653, 2007年02月28日
一般社団法人日本物理学会, 日本語

20pPSB-6 超伝導体/ハーフメタル/超伝導体接合系におけるジョセフソン効果の解析計算(領域4ポスターセッション,領域4,半導体,メゾスコピック系・局在)
澤 雄生, 浅野 泰寛, 田仲 由喜夫, 日本物理学会講演概要集, 62, 1, 686, 686, 2007年02月28日
一般社団法人日本物理学会, 日本語

18aRC-11 高温超伝導体の固有ジョセフソン接合を用いた量子ビットのデコヒーレンス評価(微小接合,領域4,半導体,メゾスコピック系・局在)
梅木 孝憲, 加藤 岳生, 田仲 由喜夫, 川畑 史郎, 柏谷 聡, 浅野 泰寛, 日本物理学会講演概要集, 62, 0, 655, 655, 2007年
一般社団法人 日本物理学会, 日本語

18aRC-2 強磁性絶縁体を介したジョセフソン電流の数値計算 : バンド構造の効果(微小接合,領域4,半導体,メゾスコピック系・局在)
川畑 史郎, 浅野 泰寛, 柏谷 聡, 田仲 由喜夫, 日本物理学会講演概要集, 62, 0, 653, 653, 2007年
一般社団法人 日本物理学会, 日本語

Smearing origin of zero-bias conductance peak in Ag-SiO-Bi 2Sr 2CaCu 2O 8+δ planar tunnel junctions: Influence of diffusive normal metal verified with the circuit theory
I. Shigeta, I. Shigeta, Y. Tanaka, Y. Tanaka, F. Ichikawa, Y. Asano, European Physical Journal B, 54, 141, 149, 2006年11月01日
We propose a new approach of smearing origins of a zero-bias conductance peak (ZBCP) in high-T c superconductor tunnel junctions through the analysis based on the circuit theory for a d-wave pairing symmetry. The circuit theory has been recently developed from conventional superconductors to unconventional superconductors. The ZBCP frequently appears in line shapes for this theory, in which the total resistance was constructed by taking account of the effects between a d-wave superconductor and a diffusive normal metal (DN) at a junction interface, including the midgap Andreev resonant states (MARS), the coherent Andreev reflection (CAR) and the proximity effect. Therefore, we have analyzed experimental spectra with the ZBCP of Ag-SiO-Bi 2Sr 2CaCu 2O 8+δ (Bi-2212) planar tunnel junctions for the 110-oriented direction by using a simplified formula of the circuit theory for d-wave superconductors. The fitting results reveal that the spectral features of the ZBCP are well explained by the circuit theory not only excluding the Dynes's broadening factor but also considering only the MARS and the DN resistance. Thus, the ZBCP behaviors are understood to be consistent with those of recent studies on the circuit theory extended to the systems containing d-wave superconductor tunnel junctions. © EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006., 機関テクニカルレポート，技術報告書，プレプリント等

Ag‐SiO‐Bi₂Sr₂CaCu₂O_8+δ積層型トンネル接合におけるゼロバイアスコンダクタンスピークのブロードニングの起源—回路理論による拡散的常伝導体の影響の検証—
重田出, 田仲由喜夫, 市川聡夫, 浅野泰寛, 米田正, 熊本電波工業高等専門学校研究紀要(CD−ROM), 33, 67-80, 2006年11月
日本語

Electronic structures and NMR T-1(-1) in quasi-one-dimensional organic superconductor (TMTSF)(2)PF6
M. Takigawa, M. Ichioka, K. Kuroki, Y. Tanaka, Y. Asano, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 445, 190, 193, 2006年10月
On the basis of the Bogoliubov de Gennes theory, electronic structures around a vortex in quasi-one-dimensional organic superconductor (TMTSF)(2)PF6 are studied at the quarter-filling electron density in magnetic fields applied parallel to the conduction chain. We consider three pairing symmetries (d-, p- and f-wave) in superconductors. In d- and f-wave symmetries, nuclear relaxation rate T-1(-1) is proportional to temperatures because quasiparticles around the vortex relax spins. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Josephson current between p-wave superconductors
Takehito Yokoyama, Yukio Tanaka, Alexander Golubov, Yasuhiro Asano, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 445, 963, 966, 2006年10月
Josephson current in p-wave superconductor/diffusive normal metal (DN)/p-wave superconductor junctions is calculated by solving the Usadel equation under the Nazarov's boundary condition extended to unconventional superconductors by changing the heights of the insulating barriers at the interfaces, the magnitudes of the resistance in DN, and the angles between the normal to the interface and the lobe directions of p-wave pair potentials. It is shown that the magnitude of the Josephson current strongly depends on the lobe directions of the p-wave pair potentials and the resulting magnitude of the Josephson current is large compared to that in the s-wave superconducting junctions due to the formation of the resonant states peculiar to p-wave superconductors. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

25aZG-3 d波超伝導体接合における強磁性体を流れるジョセフソン電流(25aZG 磁束・接合系など(理論),領域8(強相関係:高温超伝導,強相関f電子系など))
横山 毅人, 田仲 由喜夫, Golubov Alexander, 浅野 泰寛, 澤 雄生, 日本物理学会講演概要集, 61, 2, 485, 485, 2006年08月18日
一般社団法人日本物理学会, 日本語

Theory of macroscopic quantum tunneling in high-T-c cuprate
S Kawabata, Y Tanaka, S Kashiwaya, Y Asano, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 437-38, 140, 144, 2006年05月
To reveal macroscopic quantum tunneling (MQT) in high-T-c superconductor Josephson junctions is an important issue since there is a possibility to fabricate a superconducting quantum bit by use of high T-c junctions. Using the functional integral and the instanton theory, we analytically obtain the MQT rate (the inverse lifetime of the metastable state) for the c-axis twist Josephson junctions. In the case of the zero twist angle, the system shows the super-Ohmic dissipation due to the presence of the nodal quasiparticle tunneling. Therefore, the MQT rate is suppressed compared with the finite twist angle cases. Furthermore, the effect of the zero energy bound states (ZES) on the MQT in the in-plane junctions is theoretically investigated. We obtained the analytical formula of the MQT rate and showed that the presence of the ZES at the normal/superconductor interface leads to a strong Ohmic quasiparticle dissipation. Therefore, the MQT rate is noticeably inhibited compared with the c-axis junctions in which the ZES are completely absent. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Theory of superconducting pi-qubit with a ferromagnetic insulator
Shiro Kawabata, Satoshi Kashiwaya, Yasuhiro Asano, Yukio Tanaka, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 437-38, 136, 139, 2006年05月
A strong exchange field acting on the electrons in a ferromagnet-metal (FM) provokes the damped oscillatory behavior of the superconducting order parameter. This effect is an origin of the pi-junction realization in superconductor-FM-superconductor (S-FM-S) systems. In the pi-junction SQUID, a quantum coherent two-level state (qubit) is formed without an external magnetic field. Therefore, it is believed that this system becomes a quiet qubit. In the S-FM-S systems, however, the quasiparticle excitation in FM region gives rise to a strong Ohmic dissipation, so that the coherence time becomes very short. Instead, we theoretically propose a new pi-junction qubit which consists of a superconducting ring with a ferromagnetic insulator (FI). We show that the quasiparticle dissipation of this S-FI-S ring (SQUID) is very weak. This feature and the quietness of this system make it possible to realize a qubit with long decoherence time. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

27pXF-2 超伝導体/希薄磁性半導体接合への非平衡キャリア注入効果(27pXF 超伝導・電荷密度波,領域6(金属,超低温,超伝導・密度波))
赤崎 達志, 高柳 英明, 横山 毅人, 田仲 由喜夫, Golubov Alexander, 浅野 泰寛, 柳 暁志, 宗片 比呂夫, 日本物理学会講演概要集, 61, 1, 771, 771, 2006年03月04日
一般社団法人日本物理学会, 日本語

28aTC-12 拡散的常伝導体/超伝導体接合系のコンダクタンスの温度依存性(28aTC 磁束量子・その他(理論),領域8(強相関系:高温超伝導,強相関f電子系など))
重田 出, 横山 毅人, 浅野 泰寛, 田仲 由喜夫, 日本物理学会講演概要集, 61, 1, 570, 570, 2006年03月04日
一般社団法人日本物理学会, 日本語

28aTC-9 FFLO状態におけるトンネル効果の理論(28aTC 磁束量子・その他(理論),領域8(強相関系:高温超伝導,強相関f電子系など))
田仲 由喜夫, 浅野 泰寛, 柏谷 聡, 日本物理学会講演概要集, 61, 1, 569, 569, 2006年03月04日
一般社団法人日本物理学会, 日本語

30aUE-3 擬1次元有機超伝導体のペア対称性と核磁気緩和率II(30aUE 磁束量子系(磁束電子構造),領域8(強相関系:高温超伝導,強相関f電子系など))
瀧川 光明, 浅野 泰寛, 市岡 優典, 黒木 和彦, 田仲 由喜夫, 日本物理学会講演概要集, 61, 1, 647, 647, 2006年03月04日
一般社団法人日本物理学会, 日本語

Anomalous features of the proximity effect in triplet superconductors (vol 72, pg 140503, 2005)
Y Tanaka, Y Asano, AA Golubov, S Kashiwaya, PHYSICAL REVIEW B, 73, 5, 2006年02月
AMERICAN PHYSICAL SOC, 英語, その他

30aXC-11 異方的超伝導体接合におけるゼロエネルギー束縛状態と量子散逸(30aXC 微小ジョセフソン接合,領域4(半導体,メゾスコピック系・局在))
川畑 史郎, 柏谷 聡, 浅野 泰寛, 田仲 由喜夫, 加藤 岳生, Golubov A.A., 日本物理学会講演概要集, 61, 0, 706, 706, 2006年
一般社団法人 日本物理学会, 日本語

Theory of charge transport in diffusive normal metal/unconventional superconductor junctions
Y Tanaka, Y Asano, S Kashiwaya, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 1-3, 108, 111, 2006年01月
Novel theory of charge transport which is available for both a diffusive normal metal/unconventional singlet superconductor (DN/USS) and a diffusive normal metal/triplet superconductor (DN/TS) junctions is presented based on the Keldysh-Nambu quasiclassical Green's function formalism. For DN/USS junctions, proximity effect in DN region and the mid gap Andreev resonant state (MARS) formed at the USS side of the DN/USS interface strongly compete each other. On the other hand, for DN/TS junctions, proximity effect is enhanced by the MARS. In DN/TS junction, the total resistance is drastically reduced and is completely independent of the resistance of the DN in the extreme case. We can also check this dramatic effect by numerical simulations without using quasiclassical formalism. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Proximity effect in dirty normal metals attached to p and d wave superconductors
Y Asano, Y Tanaka, S Kashiwaya, H Itoh, J Inoue, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 1-3, 77, 80, 2006年01月
The conductance in dirty normal metal/superconductor junctions is numerically studied using the recursive Green function method. The proximity effect in dirty normal metals attached to superconductors depends strongly on the pairing symmetries in superconductors because of a zero-energy state forming at junction interfaces. We show the anomalous proximity effect in a p. wave junctions. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Josephson effect in p wave superconductors through dirty normal metals
Y Asano, Y Tanaka, K Sakamoto, J Inoue, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 1-3, 91, 94, 2006年01月
The Josephson current and its fluctuations through dirty normal metals in p wave superconducting junctions are numerically studied. We discuss effects of a zero-energy state at junction interfaces and those of the proximity effect in normal metals on the Josephson current. An interplay between the two interference effects causes the anomalous current-phase relation in a p(x) wave junctions. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Tunneling spectra of high-T-c superconductors with d density wave order
Y Asano, Y Tanaka, H Tsuchiura, S Kashiwaya, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 1-3, 186, 188, 2006年01月
The conductance in normal metal/high-T-c superconductor junctions is theoretically studied using the recursive Green's function method. We consider d density wave and spin density wave subdominant orders in addition to d wave superconductivity. The results show that the conductance peak at the zero bias voltage splits into two peaks in the presence of such subdominant order parameters. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Zeeman magnetic field responses of d-wave superconductors observed by tunneling spectroscopy
H Kashiwaya, S Kashiwaya, B Prijamboedi, A Sugimoto, Kurosawa, I, K Ikeda, Y Asano, Y Tanaka, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 1-3, 350, 352, 2006年01月
Spin polarized tunneling spectroscopy was applied to optimally doped Yba(2)Cu(3)O(7-delta) (YBCO) in order to detect the quasiparticle spin properties of d-wave superconducting phase. YBCO/La0.67Sr0.33MnO3 epitaxial junctions were fabricated by PLD and photolithographic process and a magnetic field was applied to the direction parallel to the ab-plane. Both on (110) and (100) oriented junctions, the expected Zeeman splitting of conductance spectrum was not detected up to 14 T even though the conductance peaks have enough sharpness to detect the splitting. This feature is quite inconsistent with weak coupling BCS model, which takes into account of d-wave symmetry. The results are explained in terms of that the high-T-c oxides are not ordinary Fermi-liquid superconductors. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Theory of charge transport in diffusive normal metal/conventional superconductor point contacts in the presence of magnetic impurity
T Yokoyama, Y Tanaka, AA Golubov, J Inoue, Y Asano, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 1-3, 68, 71, 2006年01月
Charge transport in the diffusive normal metal/insulator/s-wave superconductor junctions is studied in the presence of the magnetic impurity for various situations, where we have used the Usadel equation with Nazarov's generalized boundary condition. It is revealed that the magnetic impurity scattering suppresses the proximity effect. Wide variety of the line shapes of the tunneling conductance is obtained. Only for high transparent junction the normalized conductance around zero voltage can be enhanced by the magnetic impurity scattering. (c) 2006 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Theoretical study of magneto-tunneling spectroscopy in high-T-c superconductors
Y Asano, Y Tanaka, S Kashiwaya, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 1-3, 178, 181, 2006年01月
Magneto-tunneling spectra in normal-metal/high-T-c superconductor junctions are theoretically studied. It is shown that the impurity scattering causes the split of the zero-bias conductance peak (ZBCP) in the absence of magnetic fields. The degree of the peak splitting increases with the increase of magnetic fields consistently with experiments. On the other hand in the absence of impurity scatterings, the ZBCP remains one peak even in high magnetic fields. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Tunneling study based on the circuit theory in d-wave superconductors
Shigeta, I, Y Asano, Y Tanaka, F Ichikawa, S Kashiwaya, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 1-3, 175, 177, 2006年01月
We propose a new interpretation about zero-bias conductance peak (ZBCP) behaviours in high-T-c superconductors. The ZBCP has been frequently observed in many tunneling spectroscopic experiments for unconventional superconductors. The ZBCP mechanism was well understood by the Andreev bound states theory for unconventional superconductors. On the other hand. the circuit theory has been recently developed from conventional superconductors to unconventional superconductors. The ZBCP often appears in this theory as well. Therefore, we have analyzed experimental spectra with the ZBCP of Bi2Sr2CaCu2O8+delta planar tunnel junctions by using both theories for d-wave paring symmetry. The experimental spectra are consistent with those of recent studies on the circuit theory for d-wave superconductors. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Macroscopic quantum tunneling and dissipation in c-axis twist Josephson junctions
S Kawabata, Y Asano, S Kashiwaya, Y Tanaka, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 1-3, 120, 122, 2006年01月
We study macroscopic quantum tunneling (MQT) in c-axis twist superconductor Josephson junctions. By using the functional integral method and the instanton theory we have obtained the analytical expression of the MQT rate (the inverse lifetime of the metastable state). In the case of the zero twist angle, we find that the system shows the super-Ohmic dissipation due to the presence of the nodal quasiparticle tunneling. Therefore, the MQT rate is strongly suppressed in compared with the finite twist angle cases. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

異方的超伝導体の物理 異方的超伝導体接合におけるトンネル効果の理論の新展開
田仲由喜夫, 浅野泰寛, 固体物理, 40, 10, 683-698, 2005年10月15日
日本語

Meissner effect in diffusive normal metal/superconductor junctions
T Yokoyama, Y Tanaka, A Golubov, J Inoue, Y Asano, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 426, Pt.1, 262, 267, 2005年10月
Meissner effect in the diffusive normal metal/insulator/s-wave superconductor junctions is studied in the presence of the magnetic impurities for various situations, where we have used the Usadel equation with Nazarov's generalized boundary condition. It is shown that the susceptibility of the diffusive normal metal for s-wave superconductor is almost independent of the height of the insulating barrier at the interface. (c) 2005 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Meissner effect in diffusive normal metal/superconductor junctions
T Yokoyama, Y Tanaka, A Golubov, J Inoue, Y Asano, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 426, Part 1, 262, 267, 2005年10月
Meissner effect in the diffusive normal metal/insulator/s-wave superconductor junctions is studied in the presence of the magnetic impurities for various situations, where we have used the Usadel equation with Nazarov's generalized boundary condition. It is shown that the susceptibility of the diffusive normal metal for s-wave superconductor is almost independent of the height of the insulating barrier at the interface. (c) 2005 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

20aPS-14 汚れた常伝導体/異方的超伝導体接合系のコンダクタンスの温度依存性(領域8ポスターセッション(低温),領域8(強相関系 : 高温超伝導,強相関f電子系など))
重田 出, 横山 毅人, 浅野 泰寛, 田仲 由喜夫, 日本物理学会講演概要集, 60, 2, 431, 431, 2005年08月19日
一般社団法人日本物理学会, 日本語

22aYJ-9 スピン3重項超伝導体接合における異常近接効果と奇周波数ペアリング(磁束量子系・近接効果(理論),領域8(強相関系 : 高温超伝導,強相関f電子系など))
田仲 由喜夫, 浅野 泰寛, 柏谷 聡, 日本物理学会講演概要集, 60, 2, 508, 508, 2005年08月19日
一般社団法人日本物理学会, 日本語

22aYJ-10 p波SNS接合における近接効果とジョセフソン効果(磁束量子系・近接効果(理論),領域8(強相関系 : 高温超伝導,強相関f電子系など))
浅野 泰寛, 田仲 由喜夫, 柏谷 聡, 日本物理学会講演概要集, 60, 2, 508, 508, 2005年08月19日
一般社団法人日本物理学会, 日本語

21aWB-10 擬1次元有機超伝導体のペア対称性と核磁気緩和率(TMTSF/TMTTF塩,領域7(分子性固体・有機導体))
瀧川 光明, 市岡 優典, 黒木 和彦, 田仲 由喜夫, 浅野 泰寛, 日本物理学会講演概要集, 60, 2, 701, 701, 2005年08月19日
一般社団法人日本物理学会, 日本語

20aWF-5 微小なp波超伝導リングのスピン流(微小ジョセフソン接合,領域4(半導体,メゾスコピック系・局在))
浅野 泰寛, 日本物理学会講演概要集, 60, 2, 528, 528, 2005年08月19日
一般社団法人日本物理学会, 日本語

20aWF-2 異方的超伝導体間を流れるジョセフソン電流(微小ジョセフソン接合,領域4(半導体,メゾスコピック系・局在))
横山 毅人, 田仲 由喜夫, Alexander Golubov, 浅野 泰寛, 日本物理学会講演概要集, 60, 2, 527, 527, 2005年08月19日
一般社団法人日本物理学会, 日本語

Tunneling effect of chiral triplet superconductors
D Tamura, Y Asano, Y Tanaka, K Kuroki, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 66, 8-9, 1405, 1408, 2005年08月
The differential conductance in normal metal/Sr2RuO4 superconducting junctions is theoretically studied. We consider three types of chiral p-wave symmetries in ruthenate such as kx + ik(y), sin(k(x)) + i sin(k(y)) and sin(k(x) + k(y)) + i sin(k(x) - k(y)). Contrary to the first simple pair potential, the conductance for the second and the third pair potentials do not always have a zero bias conductance peak. In addition, the conductance line shapes depend seriously on the misorientation angles of junctions and the shape of the Fermi surface. (c) 2005 Published by Elsevier Ltd., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Zero-bias conductance peak reduction by diffusive normal metal in high-T-c superconductor tunnel junctions
Shigeta, I, Y Tanaka, F Ichikawa, Y Asano, S Kashiwaya, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 66, 8-9, 1401, 1404, 2005年08月
We report investigations of the smearing origin about a zero-bias conductance peak (ZBCP) observed in high-T-c superconductor (HTSC) tunnel junctions from the point of view of the circuit theory analysis for d-wave superconductors. The ZBCP enhancement was measured in Bi2Sr2CaCU2O8+delta-SiO-Ag planar tunnel junctions only for ab-plane directions. On the other hand, the circuit theory has been recently generalized from conventional superconductors to unconventional superconductors. The analysis in terms of the circuit theory reveals that the tunneling spectral behaviors of the ZBCP were well explained even when the Dynes's broadening factor was excluded from a tunneling spectral formula. Thus, the smearing effect in the ZBCP is understood by the influence of a diffusive normal metal resistance in the systems of HTSC tunnel junctions. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Wiedemann-Franz law in proximity bilayers
T Yokoyama, Y Tanaka, A Golubov, J Inoue, Y Asano, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 66, 8-9, 1398, 1400, 2005年08月
Wiedemann-Franz law in the diffusive normal metal/insulator/d-wave superconductor junctions is studied for various transparency of the insulating barrier and various misorientation angles between the normal to the interface and the crystal axis of d-wave superconductors. Contrary to the conductance, the thermal conductance of the junctions does not depend seriously on the misorientation angle a of the junctions. Reflecting the formation of the midgap Andreev resonant states at the junction interface, the temperature dependence of the Lorentz ratio depends drastically on alpha for low transparent junctions. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

Meissner effect in diffusive normal metal/d-wave superconductor junctions
T Yokoyama, Y Tanaka, A Golubov, J Inoue, Y Asano, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 66, 8-9, 1395, 1397, 2005年08月
The Meissner effect in diffusive normal metal/insulator/d-wave superconductor junctions is studied theoretically in the framework of the Usadel equation under the generalized boundary condition. The effect of midgap Andreev resonant states (MARS) formed at the interface of d-wave superconductor is taken into account. It is shown that the formation of MARS suppresses the susceptibility of the diffusive normal metal. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, 英語

27aWM-11 カイラル型Triplet超伝導体のトンネル効果(コバルト,ルテニウム酸化物他(理論),領域8(強相関系:高温超伝導,強相関f電子系など))
田村 大吾, 浅野 泰寛, 田仲 由喜夫, 黒木 和彦, 日本物理学会講演概要集, 60, 1, 609, 609, 2005年03月04日
一般社団法人日本物理学会, 日本語

27aWM-9 Sr_2RuO_4/s波超伝導体のSQUID(コバルト,ルテニウム酸化物他(理論),領域8(強相関系:高温超伝導,強相関f電子系など))
浅野 秦寛, 田仲 由喜夫, Sigrist M., 柏谷 聡, 日本物理学会講演概要集, 60, 1, 608, 608, 2005年03月04日
一般社団法人日本物理学会, 日本語

Influence of magnetic impurities on charge transport in diffusive-normal-metal/superconductor junctions
T Yokoyama, Y Tanaka, AA Golubov, J Inoue, Y Asano, PHYSICAL REVIEW B, 71, 9, 94506, 94509, 2005年03月
Charge transport in the diffusive normal metal (DN)/insulator/s- and d-wave superconductor junctions is studied in the presence of magnetic impurities in DN in the framework of the quasiclassical Usadel equations with the generalized boundary conditions. The cases of s- and d-wave superconducting electrodes are considered. The junction conductance is calculated as a function of a bias voltage for various parameters of the DN metal, resistivity, Thouless energy, the magnetic impurity scattering rate, and the transparency of the insulating barrier between DN and a superconductor. It is shown that the proximity effect is suppressed by magnetic impurity scattering in DN for any value of the barrier transparency. In low-transparent s-wave junctions this leads to the suppression of the normalized zero-bias conductance. In contrast to that, in high transparent junctions zero-bias conductance is enhanced by magnetic impurity scattering. The physical origin of this effect is discussed. For the d-wave junctions, the dependence on the misorientation angle a between the interface normal and the crystal axis of a superconductor is studied. The zero-bias conductance peak is suppressed by the magnetic,impurity scattering only for low transparent junctions with alpha similar to 0. In other cases the conductance of the d-wave junctions does not depend on the magnetic impurity scattering due to strong suppression of the proximity effect by the midgap Andreev resonant states., AMER PHYSICAL SOC, 英語

26pYT-13 超電導/強磁性体接合系における巨視的量子現象(微小超伝導体,領域4(半導体, メゾスコピック系・局在))
川畑 史郎, 柏谷 聡, 浅野 泰寛, 田仲 由喜夫, 日本物理学会講演概要集, 60, 0, 652, 652, 2005年
一般社団法人 日本物理学会, 日本語

22pPSA-82 微小高温超伝導体ジョセフソン接合における相転移(領域4ポスターセッション,領域4(半導体,メゾスコピック系・局在))
川畑 史郎, 柏谷 聡, 加藤 岳生, Asano Y., 田仲 由喜夫, 日本物理学会講演概要集, 60, 0, 558, 558, 2005年
一般社団法人 日本物理学会, 日本語

Mesoscopic superconductivity with unconventional superconductor or ferromagnet: Circuit theory analysis of ab-plane tunnel junctions of unconventional superconductor BI2SR2CACU2O8+δ
Iduru Shigeta, Yukio Tanaka, Yukio Tanaka, Yukio Tanaka, Fusao Ichikawa, Yasuhiro Asano, Satoshi Kashiwaya, Realizing Controllable Quantum States: Mesoscopic Superconductivity and Spintronics - In the Light of Quantum Computation, 161, 166, 2005年01月01日
© 2005 by World Scientific Publishing Co. Pte. Ltd. We report analysis of experimental tunneling spectra with a zero-bias conductance peak (ZBCP) of Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212) planar type junctions by using a simplified formula for the circuit theory based on the d-wave pairing symmetry. The circuit theory has been recently generalized from conventional superconductors to unconventional superconductors. The ZBCP frequently appears in tunneling spectra for this theory, in which the total resistance was constructed by resistances between a d-wave superconductor and a diffusive normal metal at a junction interface. The experimental tunneling spectra are consistent with those of recent studies on the circuit theory.

Conductance in normal-metal/PrOs4Sb12
Y Asano, Y Tanaka, Y Matsuda, H Tsuchiura, S Kashiwaya, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 412, Pt.1, 235, 239, 2004年10月
The tunnel conductance in normal-metal/insulator/PrOS4Sb12 junctions is theoretically studied, where skutterudite PrOs(4)Ob(12) is considered to be an unconventional superconductor. The conductance is calculated for several pair potentials which have been proposed in recent papers. The results show that the conductance spectra are sensitive to the relation between the direction of electric currents and the position of point nodes. Generally speaking, the tunnel spectra are believed to reflect the density of states in superconductor. The calculated results, however, often deviate from the shape of bulk density of states. (C) 2004 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Zero-bias peak in tunneling superconductors and spectra of high-T-c its splitting
Y Asano, R Sekiguchi, Y Tanaka, H Tsuchiura, S Kashiwaya, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 412, Pt.1, 157, 161, 2004年10月
Effects of impurities on the conductance in normal-metal/d-wave superconductor junctions are discussed. By using the single-site approximation, it is shown that the impurity scattering causes the split of the zero-bias conductance peak (ZBCP). So far, the split of the ZBCP at the zero magnetic field has been believed to be a strong evidence of the broken time reversal symmetry states at a surface of a high-T-e, superconductor. However we conclude that the impurity scattering is also responsible for the split of the ZBCP. (C) 2004 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Mesoscopic fluctuations of Josephson current in high-T-c superconductor junctions
K Sakamoto, Y Asano, Y Tanaka, H Tsuchiura, J Inoue, S Kashiwaya, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 412, Pt.1, 221, 224, 2004年10月
The dc Josephson current and its fluctuations in superconductor/dirty normal metal/superconductor junctions are studied numerically by using the recursive Green function method, where a d-wave pairing symmetry is assumed in superconductors as it is in high-T-c materials. The Josephson current is sensitive to the orientation angle (alpha) between the crystalline axis of the high-T-c superconductors and the normal of the junction interface. When the orientation angle is pi/4, the fluctuations of the Josephson current become larger than those with alpha = 0 because of the zero-energy state formed at junction interfaces. (C) 2004 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Tunneling effect in triangular lattice superconductor NaxCoO2
Y Asano, Y Tanaka, K Kuroki, Y Tanuma, H Tsuchiura, S Kashiwaya, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 412, Pt.1, 187, 191, 2004年10月
The tunnel conductance in normal-metal/NaxCoO2 is studied theoretically, where NaCoO2 is a new superconductor discovered in a recent experiment. So far, it has been pointed out that superconductivity is characterized by an unconventional pairing symmetry and that the chiral symmetry may be broken down in the superconducting phase of NaxCoO2. Theoretical studies have suggested p, d and f wave pairing symmetries. We calculate the differential conductance of NaxCoO2 within the quasiclassical approximation by assuming the chiral p, chiral d and f wave symmetries. The results show the zero-bias conductance peak in the case of p and f wave symmetries in tunnel spectra. (C) 2004 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

12aTM-4 磁性不純物を含む汚れた常伝導体/超伝導体接合系における輸送現象の理論的研究(超伝導, 領域 6)
横山 毅人, 田仲 由喜夫, 井上 順一郎, 浅野 泰寛, 日本物理学会講演概要集, 59, 2, 696, 696, 2004年08月25日
一般社団法人日本物理学会, 日本語

13pYD-3 Impurity Scattering in Unconventional Superconductor Junctions(Progress in physics of superconducting junctions : phase, spin and control of quantum interference)
Asano Yasuhiro, 日本物理学会講演概要集, 59, 2, 510, 510, 2004年08月25日
一般社団法人日本物理学会, 英語

12aWD-13 p 波超伝導体の SNS 接合における異常なジョセフソン効果(コバルト酸化物・Triplet 超伝導 : 理論, 領域 8)
浅野 泰寛, 田仲 由喜夫, 日本物理学会講演概要集, 59, 2, 429, 429, 2004年08月25日
一般社団法人日本物理学会, 日本語

Josephson effect in quasi one-dimensional unconventional superconductors
Y Asano, Y Tanaka, Y Tanuma, K Kuroki, H Tsuchiura, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73, 7, 1922, 1930, 2004年07月
Josephson effect in junctions of quasi one-dimensional superconductors at the quarter-filling electron density is discussed by using the tight-binding model on a two-dimensional square lattice. To consider the triangular lattice structures in real materials such as (TMTSF)(2)X (X = PF6, ClO4, etc), the asymmetric hopping integral is introduced among second nearest lattice sites. A combination of these characters in superconductors (quasi one-dimensionality, quarter-filling electron density and weak triangular lattice structures) seriously affects the formation of a zero-energy state at a junction interface. As a consequence, calculated results of the Josephson current show anomalous dependences on temperatures., PHYSICAL SOC JAPAN, 英語

銅酸化物超伝導体におけるJosephson効果
浅野泰寛, 田仲由喜夫, 柏谷聡, 豊田研究報告, 57, 1-7, 7, 2004年05月30日
豊田理化学研究所, 日本語

27aXA-5 擬1次元有機超伝導体のジョセフソン効果(高温超伝導理論・低次元系理論)(領域8)
浅野 泰寛, 田仲 由喜夫, 田沼 慶忠, 黒木 和彦, 土浦 宏紀, 日本物理学会講演概要集, 59, 1, 509, 509, 2004年03月03日
一般社団法人日本物理学会, 日本語

2004年の化学 注目の論文 三角格子酸化物における超伝導の発見 フラストレートした系で期待される異方的超伝導状態
田仲由喜夫, 浅野泰寛, 化学, 59, 2, 54-55, 2004年02月01日
日本語

12pYB-1 異方的超伝導体ジョセフソン接合における巨視的量子トンネルと摩擦 2(微小超伝導・微小ジョセフソン接合, 領域 4)
川畑 史郎, 柏谷 聡, 浅野 泰寛, 田仲 由喜夫, 日本物理学会講演概要集, 59, 0, 587, 587, 2004年
一般社団法人 日本物理学会, 日本語

27pYG-13 異方的超伝導体ジョセフソン接合における巨視的量子トンネルと摩擦(微小金属/超伝導体/ジョセフソン結合)(領域4)
川畑 史郎, 柏谷 聡, 浅野 泰寛, 田仲 由喜夫, 日本物理学会講演概要集, 59, 0, 679, 679, 2004年
一般社団法人 日本物理学会, 日本語

13aRA-3 Bi_2Sr_2CaCu_2O_<8+δ>-SiO-Ag 積層型接合におけるトンネルスペクトルのサーキノト理論による解析(高温超伝導 : トンネル分光, 領域 8)
重田 出, 田仲 由喜夫, 市川 聡夫, 浅野 泰寛, 柏谷 聡, 日本物理学会講演概要集, 59, 0, 2004年
一般社団法人 日本物理学会, 日本語

21pTM-12 d 波超伝導体 SNS 接合のジョセフソン電流
坂元 圭, 浅野 泰寛, 田仲 由喜夫, 井上 順一郎, 日本物理学会講演概要集, 58, 2, 493, 493, 2003年08月15日
一般社団法人日本物理学会, 日本語

21pTM-11 高温超伝導体におけるゼロバイアスコンダクタンスピークの分裂
浅野 泰寛, 田仲 由喜夫, 柏谷 聡, 日本物理学会講演概要集, 58, 2, 492, 492, 2003年08月15日
一般社団法人日本物理学会, 日本語

22pWG-8 スックテルダイト PrOs_4Sb_<12> のトンネルスペクトル
浅野 泰寛, 田仲 由喜夫, 松田 祐司, 柏谷 聡, 日本物理学会講演概要集, 58, 2, 550, 550, 2003年08月15日
一般社団法人日本物理学会, 日本語

Effects of spin-orbit scattering on Josephson current between s-wave superconductor and Sr2RuO4
Y Asano, T Hirai, Y Tanaka, J Inoue, M Sigrist, S Kashiwaya, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388, 505, 506, 2003年05月
The Josephson effect in s-wave superconductor/insulator/Sr2RuO4 (S/I/SRO) junctions is studied. We focus on influences of spin-orbit scattering at the junction interface on the phase-current relationship in the Josephson current. In the presence of the spin-orbit scattering, we find that the Josephson current has a term which is proportional to cos phi, where phi is the phase-difference between S and SRO. (C) 2003 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Zero-bias conductance peak in disordered ferromagnetic metal/d(x2-y2)-wave superconductor junction
N Yoshida, H Itoh, Y Asano, Y Tanaka, J Inoue, S Kashiwaya, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388, 96, 97, 2003年05月, ［査読有り］
We investigate numerically the spin-polarized tunneling effect in ferromagnetic metal/insulator/d(x2-y2)-wave super-conductor junctions. It is shown that the height of the zero-bias conductance peak owing to the zero energy states is depending on the magnitude of the exchange potential and the randomness near the junction interface. (C) 2003 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

28pWF-11 s-波超伝導体/Sr_2RuO_4 接合のジョセフソン電流
浅野 泰寛, 田仲 由喜夫, Sigrist M., 柏谷 聡, 日本物理学会講演概要集, 58, 1, 519, 519, 2003年03月06日
一般社団法人日本物理学会, 日本語

異方的超伝導体のジョセフソン効果
浅野泰寛, 田仲由喜夫, 柏谷聡, 固体物理, 38, 2, 125-139, 139, 2003年02月15日
アグネ技術センタ-, 日本語

9pXA-1 常伝導体-高温超伝導体接合におけるアンドレーフ共鳴準位の分裂(高温超伝導・理論(トンネル,超伝導機講),領域8)
浅野 秦寛, 田仲 由喜夫, 日本物理学会講演概要集, 57, 2, 541, 541, 2002年08月13日
一般社団法人日本物理学会, 日本語

9pXA-3 銅酸化物超伝導体接合におけるドップラー効果の理論(高温超伝導・理論(トンネル,超伝導機講),領域8)
田仲 由喜夫, 伊藤 博介, 浅野 泰寛, 田沼 慶忠, 土浦 宏紀, 井上 順一郎, 柏谷 聡, 日本物理学会講演概要集, 57, 2, 542, 542, 2002年08月13日
一般社団法人日本物理学会, 日本語

7aQB-5 超伝導ジョセフソン接合系の理論の最近の進展(CDW・超伝導,領域6)
浅野 泰寛, 日本物理学会講演概要集, 57, 2, 659, 659, 2002年08月13日
一般社団法人日本物理学会, 日本語

7aSA-14 アンダーソン絶縁体を介したジョセフソン電流(量子ドット・微小ジョセフソン接合・微小SN接合,領域4)
浅野 泰寛, 日本物理学会講演概要集, 57, 2, 566, 566, 2002年08月13日
一般社団法人日本物理学会, 日本語

27pWA-4 異方的超伝導体のSNS接合におけるジョセフソン電流II(27pWA 高温超伝導・理論(トンネル),領域8(強相関系分野-高温超伝導,強相関f電子系など))
浅野 泰寛, 日本物理学会講演概要集, 57, 1, 589, 589, 2002年03月01日
一般社団法人日本物理学会, 日本語

27pWA-5 スピン3重項超伝導体Sr_2RuO_4のジョセフソン電流(27pWA 高温超伝導・理論(トンネル),領域8(強相関系分野-高温超伝導,強相関f電子系など))
片淵 啓介, 浅野 泰寛, 日本物理学会講演概要集, 57, 1, 589, 589, 2002年03月01日
一般社団法人日本物理学会, 日本語

A numerical study of dc Josephson effect in SNS junctions of d-wave superconductors
Y Asano, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 367, 1-4, 157, 160, 2002年02月
We numerically study the de Josephson current in d-wave superconductor/normal metal/d-wave superconductor junctions by using the recursive Green function method. The Josephson current is sensitive to the orientation angle between the crystalline axis of the high-T-c superconductors and the normal of the junction interface. It was pointed out that the ensemble average of the Josephson current, (J), vanishes when the orientation angle is pi/4 and the normal metal is in the diffusive transport regime. We show in this paper that (J) disappears even when the normal metal is in the quasi-ballistic transport regime. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Symmetry of pair potential and Josephson effect in dirty SNS junctions
Y Asano, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 367, 1-4, 92, 98, 2002年02月
We derive a formula of the dc Josephson current between two superconductors with the anisotropic pairing symmetry. One of the basic characters in the junctions of the anisotropic superconductors is the formation of the zero-energy bound states at the junction interfaces, which leads to the low-temperature anomaly of the Josephson current. The contribution of the zero-energy states to the Josephson current is fully taken into account in the present formalism. We apply the formula to superconductor/dirty normal conductor/superconductor junctions. It is found that the ensemble average of the Josephson current vanishes when the junction interface is perpendicular to a plane which includes the node lines of the quasiparticle's excitation gap. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

17aYB-9 異方的超伝導体のSNS接合におけるジョセフソン電流
浅野 泰寛, 日本物理学会講演概要集, 56, 2, 380, 380, 2001年09月03日
一般社団法人日本物理学会, 日本語

28pPSB-12 構造を有する系における常伝導体/d-波超伝導体接合界面の量子干渉効果
元木 伸治, 野々山 信二, 浅野 泰寛, 日本物理学会講演概要集, 56, 1, 536, 536, 2001年03月09日
一般社団法人日本物理学会, 日本語

30pYL-6 d波超伝導体のSNS接合におけるジョセフソン効果
浅野 泰寛, 日本物理学会講演概要集, 56, 1, 581, 581, 2001年03月09日
一般社団法人日本物理学会, 日本語

半導体細線‐超伝導体接合における磁気コンダクタンス振動
浅野泰寛, 日本物理学会講演概要集, 54, 2, 620, 620, 1999年09月03日
一般社団法人日本物理学会, 日本語

バリスティック半導体‐超伝導体接合におけるアハロノフ・ボーム振動
浅野泰寛, 加藤太一郎, 日本物理学会講演概要集, 54, 1, 577, 577, 1999年03月15日
一般社団法人日本物理学会, 日本語

Phase shift of an electron wave through a quantum dot and Aharonov-Bohm effect
Y Asano, M Ohi, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 38, 1B, 392, 395, 1999年01月
The transmission coefficients of an electron wave passing through an Aharonov-Bohm (AB) ring with a quantum dot in one of its arms are studied numerically by the recursive Green function method. In addition to lead wires which are used as the current-voltage probes, several lead wires are attached to the AB ring in a simulation as they are in an experiment. We discuss the relation ship between the effects of the additional lead wires on the electron transmission and the validity of a simple current formula which has been employed in a number of studies. We conclude that the simple current formula is valid when the additional lead wires are strongly coupled to the AB ring., JAPAN J APPLIED PHYSICS, 英語

縦型2重量子ドットにおける電子状態と輸送現象
浅野泰寛, 物性研だより, 38, 5, 17-18, 1999年01月
日本語

量子ドットを含むアハロノフ・ボームリングにおける電子波の位相シフト
浅野泰寛, 大井雅史, 日本物理学会講演概要集, 53, 2, 713, 713, 1998年09月05日
一般社団法人日本物理学会, 日本語

Quasi-ballistic conductance fluctuations and ergodic hypothesis
Y Asano, GEW Bauer, PHYSICA B-CONDENSED MATTER, 249, 523, 526, 1998年06月
We study the conductance fluctuations in the quasi-ballistic transport regime by an analytical method based on the Lippmann-Schwinger equation and the Landauer formula. The contribution of single impurity scattering events, impurity potential fluctuations, multiple scattering between an impurity and sample boundaries as well as multiple scattering involving many impurities are discussed. The amplitude of the fluctuations cannot be measured by tuning the Fermi energy or an external magnetic field because the single impurity scattering events dominate the fluctuations, implying that the ergodic hypothesis breaks down in the quasi-ballistic transport regime. Absence of aperiodic oscillations in the experimental parametric conductance does not always mean an absence of defects in the sample. (C) 1998 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

量子ドット分子の電子状態 II
浅野泰寛, 日本物理学会講演概要集(年会), 53, 1, 622, 1998年03月
日本語

二つの量子ドットにおける電子状態
浅野泰寛, 日本物理学会講演概要集(分科会), 1997, 141, 1997年09月
日本語

金属ヘテロポイントコンタクトにおける伝導率揺らぎ
浅野泰寛, BAUER G E W, 日本物理学会講演概要集(分科会), 1996, Autumn Pt 3, 414, 1996年09月
日本語

A theory of conductivity for perpendicular currents through a single random interface
H Itoh, J Inoue, Y Asano, S Maekawa, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 156, 1-3, 343, 344, 1996年04月
A perpendicular conductance through a single resistive layer is formulated in the coherent potential approximation (CPA). Vertex corrections are evaluated exactly within CPA. Calculated results are compared with those obtained by numerical simulations in finite systems. The physical implication of the result is discussed., ELSEVIER SCIENCE BV, 英語

バリスティック伝導領域近傍における伝導率ゆらぎ
浅野泰寛, BAUER G E W, 日本物理学会講演概要集(年会), 51st, 3, 314, 1996年03月
日本語

磁性超微粒子合金における巨大磁気抵抗の理論 III
浅野泰寛, 小栗章, 井上順一郎, 前川禎通, 日本物理学会講演概要集(年会), 50th, 3, 35, 1995年03月
日本語

NUMERICAL STUDY OF MAGNETORESISTANCE IN GRANULAR ALLOYS
Y ASANO, A OGURI, J INOUE, S MAEKAWA, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 140, Pt 1, 505, 506, 1995年02月
Numerical simulation of giant magnetoresistance in magnetic granular alloys is performed by using the recursive Green's function method and the Kubo formula. It is shown that the magnetoresistance depends on the shape of magnetic clusters and that classical cross-section of clusters is a crucial factor for the magnetoresistance., ELSEVIER SCIENCE BV, 英語

磁性超微粒子合金における磁気抵抗の理論 II
浅野泰寛, 小栗章, 井上順一郎, 前川禎通, 日本物理学会講演概要集(年会), 49th, 3, 38, 1994年03月
日本語

量子細線における電子相関の効果
野々山信二, 小栗章, 浅野泰寛, 前川禎通, 日本物理学会講演概要集(年会), 49th, 3, 278, 1994年03月
日本語

Giant magnetoresistance in magnetic granular alloys
Y. Asano, A. Oguri, J. Inoue, S. Maekawa, Physical Review B, 49, 18, 12831, 12834, 1994年01月01日
Numerical simulation on resistance and giant magnetoresistance in magnetic granular alloys is performed for finite-size systems by making use of the real-space Green's-function method based on the Kubo formalism. Spin-dependent scattering causes the giant magnetoresistance in the magnetic granular alloys as in the magnetic multilayers. It is shown by using the microscopic theory that the magnetoresistance increases with decreasing the size of magnetic grains, in agreement with experiment. The theoretical results indicate that scattering at the surfaces of magnetic grains governs the resistance and magnetoresistance in granular alloys. Difference between the giant magnetoresistances in the granular alloys and multilayers is discussed. © 1994 The American Physical Society.

Numerical study of the effect of Coulomb repulsion on resonant tunneling
Shinji Nonoyama, Akira Oguri, Yasuhiro Asano, Sadamichi Maekawa, Physical Review B, 50, 4, 2667, 2670, 1994年01月01日
The effect of on-site Coulomb repulsion on the process of resonant tunneling is studied in the tight-binding model of a quasi-one-dimensional system. The conductance through a small region where the Coulomb interaction is strong is calculated as a function of chemical potential with use of the Kubo formula. The Green's function and the number of electrons in the region are obtained self-consistently using the recursion method in the mean-field approximation. It is found that the conductance shows various doublet structures depending on the broadening of the virtual bound state and the Coulomb interaction. © 1994 The American Physical Society.

NUMERICAL STUDY OF THE CONDUCTANCE IN MAGNETIC SUPERLATTICES
Y ASANO, A OGURI, S MAEKAWA, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 126, 1-3, 482, 484, 1993年09月
Effects of the multilayered structure on the conductance in magnetic superlattices is studied numerically based on the Kubo formula by use of the recursion method. The results for the magnetoresistance of Fe/Cr superlattices for the current parallel and perpendicular to the layers are presented., ELSEVIER SCIENCE BV, 英語

磁性超微粒子合金における巨大磁気抵抗の理論
浅野泰寛, 小栗章, 井上順一郎, 前川禎通, 日本物理学会講演概要集(分科会), 1993, Autumn Pt 3, 39, 1993年09月
日本語

Parallel and perpendicular transport in multilayered structures
Y. Asano, A. Oguri, S. Maekawa, Physical Review B, 48, 9, 6192, 6198, 1993年01月01日
The difference between parallel and perpendicular conductance in magnetic superlattices such as Fe/Cr are studied numerically with the Kubo formula and a recursion method. In the calculation, the multilayered structure of superlattices is taken into account through a periodic potential along the direction normal to the interfaces. It is shown that the magnetoresistance for the current parallel to the layers MR is increased by the interface roughness and decreased by the bulk impurity scattering. Since the Brillouin zone is divided into a series of minizones due to the periodic potential, the magnetoresistance for the current perpendicular to the layers MR is determined by the miniband structure and becomes larger than MR. © 1993 The American Physical Society.

超格子のコンダクタンスの数値計算
浅野泰寛, 小栗章, 前川禎通, 日本物理学会講演概要集(分科会), 1992, Autumn Pt 3, 366, 1992年09月
日本語

超格子のコンダクタンスの転送行列法による解析
浅野泰寛, 小栗章, 前川禎通, 日本物理学会講演概要集(年会), 47th, 2, 154, 1992年03月
日本語

量子細線の磁気伝導度
小栗章, 浅野泰寛, 前川禎通, 日本物理学会講演概要集(分科会), 1991, Spring Pt 3, 303, 1991年03月
日本語

Andreev Reflection in Superconducting Junctions　　　　　　　　　　　　　　　
Yasuhiro Asano
Springer(ISBN:978-981-16-4165-7), 2021年11月, ［単著］

Fundamentals and Frontiers of the Josephson Effect　　　　　　　　　　　　　　　
Yasuhiro Asano, Yukio Tanaka, Sec. 4 Charge Transport in Unconventional Superconductor Junctions
Springer, 2019年08月, 9783030207267, 英語, 教科書・概説・概論, ［分担執筆］

Anomalous proximity effect due to odd-frequency Cooper pairs　　　　　　　　　　　　　　　
Yasuhiro Asano
Workshop on Mesoscopic Superconductivity and Quantum Transport, 2023年10月13日, 英語, 口頭発表（招待・特別）
2023年10月13日 - 2023年10月13日, ［招待講演］

Josephson Effect of two-band/orbital superconductors　　　　　　　　　　　　　　　
Y. Asano
Topological Superconductivity in Quantum Materials, 2020年10月19日, 英語, 口頭発表（招待・特別）
2020年10月19日 - 2020年10月22日, ［招待講演］

Nonlocal conductance due to a chiral edge mode　　　　　　　　　　　　　　　
Yasuhiro Asano
Oxide Superspin Workshop 2019, 2019年07月25日, 英語, 口頭発表（招待・特別）
2019年07月24日 - 2019年07月28日, ［招待講演］

Flat-band Andreev bound states and odd-frequency Cooper pairs　　　　　　　　　　　　　　　
Yasuhiro Asano
Majorana Fermions and topological Material Science, 2018年07月26日, 英語, 口頭発表（招待・特別）
Ettore Majorana Foundation and Centre for Scientific Culture,\\ Erice, Sicily, Italy, ［招待講演］, ［国際会議］

Dirty two-band superconductivity　　　　　　　　　　　　　　　
Yasuhiro Asano
Oxide Superconducting spintronics 2017, 2017年11月26日, 英語, 口頭発表（招待・特別）
Yukawa Institute for Theoretical Physics, Kyoto Univ., Japan, ［招待講演］, ［国際会議］

Flat-band Andreev bound states and odd-frequency Cooper pairs　　　　　　　　　　　　　　　
Yasuhiro Asano
Novel Quantum States in Condensed Matter 2017, 2017年11月16日, 英語, 口頭発表（招待・特別）
Yukawa Institute for Theoretical Physics, Kyoto Univ., Japan, ［招待講演］, ［国際会議］

Dirty two-band superconductivity　　　　　　　　　　　　　　　
Yasuhiro Asano
The 6th International Conference on Mesoscopic Structures: Fundamentals and Applications, 2017年07月09日, 英語, 口頭発表（招待・特別）
Hotel “Baikal”, Listvyanka, Irkutsk region, Russia, ［招待講演］, ［国際会議］

Anomalous magnetic response and electric transport due to odd-frequency Cooper pair　　　　　　　　　　　　　　　
Yasuhiro Asano
International Conference on Superconducting hybrid nanostructures: physics and application, 2016年09月23日, 英語, 口頭発表（招待・特別）
Moscow Institute of Physics and Technology, Dolgoprudny, Russia,, ［招待講演］, ［国際会議］

Edge current in a small chiral superconductor　　　　　　　　　　　　　　　
Yasuhiro Asano
SPIE. photonics and spintronics 2016, 2016年09月01日, 英語, 口頭発表（招待・特別）
San Diego Convention center, San Diego, U. S. A., ［招待講演］, ［国際会議］

Paramagnetic response of small topological superconductors　　　　　　　　　　　　　　　
Yasuhiro Asano
International Conference on Interaction of Superconductivity and Magnetism in Nanosystems, 2015年09月04日, 英語, 口頭発表（基調）
Moscow State Institute of Steel and Alloys, Moscow, Russia, ［招待講演］, ［国際会議］

Anomalous proximity effect and more than one Majorana fermion　　　　　　　　　　　　　　　
Yasuhiro Asano
11th International Workshop on Nanomagnetism \& Superconductivity at the Nanoscale, 2015年07月01日, 英語, 口頭発表（招待・特別）
Nuva Hotel Comarruga, Coma-Ruga, Spain, ［招待講演］, ［国際会議］

Anomalous proximity effect and more than one Majorana fermio　　　　　　　　　　　　　　　
Yasuhiro Asano
11th International Conference on Ceramic Materials Components for Energy and Environmental Applications, 2015年06月16日, 英語, 口頭発表（招待・特別）
Hotel Hyatt Regency, Vancouver, Canada, ［招待講演］, ［国際会議］

Magnetic property of Odd-frequency Cooper Pairs　　　　　　　　　　　　　　　
Yasuhiro Asano
International Conference on Topological Quantum Phenomena, 2014年12月17日, 英語, 口頭発表（招待・特別）
Kyoto University, Kyoto, Japan,, ［招待講演］, ［国際会議］

Properties of Odd-frequency Pairs　　　　　　　　　　　　　　　
Yasuhiro Asano
日本物理学会秋の分科会, 領域6シンポジウム, 2014年09月07日, 英語, 口頭発表（招待・特別）
中部大学, 春日井, ［招待講演］, ［国内会議］

Paramagnetic Meisner Effect in Small Unconventional Superconductors　　　　　　　　　　　　　　　
Yasuhiro Asano
Physics and Applications of Superconducting Hybrid Nano-Engineered Devices, 2014年09月01日, 英語, 口頭発表（招待・特別）
Grand Hotel Santamaria, Santa Maria di Castellabate, Italy, ［招待講演］, ［国際会議］

Paramagnetic Meisner Effect in Small Unconventional Superconductors　　　　　　　　　　　　　　　
Yasuhiro Asano
10th International Workshop on Nanomagnetism \& Superconductivity at the Nanoscale, 2014年07月02日, 英語, 口頭発表（招待・特別）
Hotel Vita Comarruga, Coma-Ruga, Spain, ［招待講演］, ［国際会議］

Three-dimensional Symmetry Breaking Topological States　　　　　　　　　　　　　　　
Yasuhiro Asano
MTI and ITS Fall Workshop 2013: Coherent Hybrid Structures on the Mesoscale, 2013年10月16日, 英語, 口頭発表（招待・特別）
Hilton hotel Orrington/Evanston, Illinois, U. S. A., ［招待講演］, ［国際会議］

Surface/interfacial states of topological materials　　　　　　　　　　　　　　　
Yasuhiro Asano
Electron Correlation in nanostructures 2013, 2013年10月03日, 英語, 口頭発表（招待・特別）
Hotel Yalta-Intourist, Yalta, Ukraine, ［招待講演］, ［国際会議］

Majorana fermions and Odd-frequency Cooper Pairs　　　　　　　　　　　　　　　
Yasuhiro Asano
MTI Nonconventional Insulators Workshop 2012, 2012年11月13日, 英語, 口頭発表（招待・特別）
Argonne National Laboratory, Illinois, U. S. A., ［招待講演］, ［国際会議］

Majorana fermions and Odd-frequency Cooper Pairs　　　　　　　　　　　　　　　
Yasuhiro Asano
9th International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials, 2012年09月17日
Grand Hotel Villa Tuscolana, Roma, Italy

Majorana fermions and Odd-frequency Cooper Pairs　　　　　　　　　　　　　　　
Yasuhiro Asano
Workshop on Superconducting Nanohybrids 2012, 2012年09月05日, 英語, 口頭発表（招待・特別）
Donostia International Physics Center, San Sebastian, Spain, ［招待講演］, ［国際会議］

Odd-frequency Cooper Pairs in spin-triplet superconducting junctions　　　　　　　　　　　　　　　
Yasuhiro Asano
The International conference "Dubna-Nano2012, 2012年07月13日, 英語, 口頭発表（基調）
Bogoliubov Laboratory of Theoretical Physics, Dubna, Russia, ［招待講演］, ［国際会議］

Odd-frequency Cooper Pairs in ferromagnetic junctions　　　　　　　　　　　　　　　
Yasuhiro Asano
8th International Workshop on Nanomagnetism & Superconductivity, 2012年07月05日, 英語, 口頭発表（招待・特別）
Hotel Marvel, Coma-ruga, Spain,, ［招待講演］, ［国際会議］

Proximity Effect of Odd-frequency Cooper Pairs　　　　　　　　　　　　　　　
浅野泰寛
International Conference on Topological Phenomena, TQP2012, 2012年05月19日, 英語, 口頭発表（招待・特別）
Nagoya University, Japan, ［招待講演］, ［国際会議］

Odd-frequency Cooper Pairs and Their Effects on Surface Impedance　　　　　　　　　　　　　　　
浅野泰寛
Superconductivity and Magnetism, SM-2011, 2011年10月07日, 英語, 口頭発表（招待・特別）
Kishinev, Moldva, ［招待講演］, ［国際会議］

Anomalous Surface Impedance due to Odd-frequency Cooper Pairs　　　　　　　　　　　　　　　
浅野泰寛
7th International Workshop on Nanomagnetism \& Superconductivity, 2011年07月05日, 英語, 口頭発表（招待・特別）
Hotel Marvel, Coma-ruga, Spain, ［招待講演］, ［国際会議］

Anomalous Surface Impedance due to Odd-frequency Cooper Pairs　　　　　　　　　　　　　　　
浅野泰寛
8th International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials, 2011年06月09日, 英語, 口頭発表（招待・特別）
J. W. Marriott Hotel Chongqing, China, ［招待講演］, ［国際会議］

Tunneling between Two Helical superconductors via Majorana Edge Channels　　　　　　　　　　　　　　　
浅野泰寛
Superconductivity and Magnetism 2010, 2010年09月07日, 英語, 口頭発表（招待・特別）
Savoy Hotel, Paestum, Italy, ［招待講演］, ［国際会議］

Unusual Cooper Pairs in Superconducting Proximity Structures　　　　　　　　　　　　　　　
浅野泰寛
International Conference on Superconductivity and Magnetism 2010, 2010年04月26日, 英語, 口頭発表（招待・特別）
Porto Bello Hotel, Antalya, Turkey, ［招待講演］, ［国際会議］

Proximity effect in spin-triplet superconducting junctions　　　　　　　　　　　　　　　
浅野泰寛
nternational Symposium on Novel Spin Pairing 2009, 2009年09月14日, 英語, 口頭発表（招待・特別）
Yukawa Memorial Hall, Kyoto University, Japan, ［招待講演］, ［国際会議］

Josephson current through a strong ferromagnet　　　　　　　　　　　　　　　
浅野泰寛
International symposium on new directions of superconducting nanostructures 2009, 2009年09月05日, 英語, 口頭発表（招待・特別）
Nagoya University, Japan, ［国際会議］

Luminescence of a superconducting pn Junction　　　　　　　　　　　　　　　
浅野泰寛
Nanoscience and Engineering in Superconductivity, Hybrid and Josephson Structures, 2009年06月03日, 英語, 口頭発表（招待・特別）
Anacapri, Italy, ［国際会議］

"Josephson Effect in Chiral p-wave Superconductors　　　　　　　　　　　　　　　
浅野泰寛
Spin Helicity and Chirality in Superconductor and Semiconductor Nanostructures, 2008年07月14日, 英語, 口頭発表（招待・特別）
Karlsurhe, Germany, ［招待講演］, ［国際会議］

Conductance Spectroscopy of Spin-triplet Superconductors　　　　　　　　　　　　　　　
浅野泰寛
Probing superconductivity at the nanoscale, 2008年06月05日, 英語, 口頭発表（招待・特別）
Alicante, Spain, ［招待講演］, ［国際会議］

Odd-frequency Pairing State in Superconductor / Ferromagnet Junctions　　　　　　　　　　　　　　　
浅野泰寛
日本物理学会63回年次大会, 領域3-6シンポジウム, 2008年03月, 英語, 口頭発表（招待・特別）
近畿大学, 大阪, ［招待講演］, ［国内会議］

Conductance Spectroscopy of Spin-triplet Superconductors　　　　　　　　　　　　　　　
浅野泰寛
MTI International Argonne Fall Workshop on Nanophysics VII, 2007, 2007年12月, 英語, 口頭発表（招待・特別）
National Center for Theoretical Sciences, Hsinchu, Taiwan, ［招待講演］, ［国際会議］

Odd-frequency Cooper Pairs in Ferromagnet/Superconductor Junctions　　　　　　　　　　　　　　　
浅野泰寛
Nanoscale Superconductors and their Applications, 2007年11月, 日本語, 口頭発表（招待・特別）
Institute for Material Research in Tohoku Univ., Sendai, Japan, ［招待講演］, ［国内会議］

Josephson Current through a Strong Ferromagnet and Odd-frequency Pairs　　　　　　　　　　　　　　　
浅野泰寛
Physics of Nanoscale Superconducting Heterostructures, 2007年07月, 英語, 口頭発表（招待・特別）
Lorentz Center in Leiden Univ., Leiden, The Netherlands,, ［招待講演］, ［国際会議］

Proximity Effect in Half metals and Odd-frequency Cooper Pairs　　　　　　　　　　　　　　　
浅野泰寛
International Conference on Nanoscale Magnetism, 2007年06月, 英語, 口頭発表（招待・特別）
Istanbul, Turkey, ［招待講演］, ［国際会議］

Anomalous Josephson Effect in Unconventional Superconductor Junctions　　　　　　　　　　　　　　　
浅野泰寛
Quantum Phenomena in Low-dimensional Systems, 2007年01月, 英語, 口頭発表（招待・特別）
［招待講演］, ［国際会議］

Anomalous Proximity Effect due to Odd-Frequency Cooper Pairs　　　　　　　　　　　　　　　
浅野泰寛
Sixth International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials, 2007年01月, 英語, 口頭発表（招待・特別）
Sydney, Austraria,, ［招待講演］, ［国際会議］

Josephson Current through a Diffusive Half Metal　　　　　　　　　　　　　　　
浅野泰寛
19th International Symposium on Superconductivity, 2006年10月, 英語, 口頭発表（招待・特別）
Nagoya, Japan, ［招待講演］, ［国際会議］

Spin Current in Triplet Superconducting Rings　　　　　　　　　　　　　　　
浅野泰寛
International Conference on Nanoscale Magnetism, 2005年07月, 英語, 口頭発表（招待・特別）
［招待講演］, ［国際会議］

Impurity Effect of Unconventional Superconducting Junctions　　　　　　　　　　　　　　　
浅野泰寛
International Workshop on Physics of Superconducting pi-Phase Shift Devices, 2005年04月, 英語, 口頭発表（招待・特別）
［招待講演］, ［国際会議］

異方的超伝導体接合の不純物効果　　　　　　　　　　　　　　　
浅野泰寛
日本物理学会秋の分科会, 領域4シンポジウム, 2004年09月, 英語, 口頭発表（招待・特別）
［招待講演］, ［国内会議］

超伝導ジョセフソン接合系の理論の最近の進展　　　　　　　　　　　　　　　
浅野泰寛
日本物理学会秋の分科会, 2002年09月, 日本語, 口頭発表（招待・特別）
［招待講演］, ［国内会議］

Symmetry of Pair Potential and Josephson Effect in Dirty SNS Junctions}　　　　　　　　　　　　　　　
浅野泰寛
The International Symposium on Superconducting Device Physics, 2001年06月15日, 英語, 口頭発表（招待・特別）
［招待講演］, ［国際会議］

多自由度を持つ電子系の超伝導体における奇周波数電子対の物理
文部省科学研究費補助金(基盤研究(B))
2020年04月 - 2023年03月
浅野泰寛、田仲由喜夫、水島健
日本学術振興会, 基盤研究（B)（一般）, 北海道大学, 研究代表者

強相関物質のトポロジカル相　　　　　　　　　　　　　　　
科学研究費補助金（新学術領域研究）
2015年 - 2019年
川上則雄
文部科学省, 研究分担者, 競争的資金

トポロジカル絶縁体/超伝導体接合におけるスピン流を用いた熱制御デバイスの理論
科学研究費助成事業
2015年04月01日 - 2018年03月31日
川畑 史郎, 浅野 泰寛, 富永 淳二
トポロジカル物質と超伝導体が接合した系における量子及び熱輸送理論の構築を行った。具体的にはワイル半金属/超伝導体接合の熱輸送シミュレーションを行い、スピンー運動量ロッキングによってAndreev反射が抑制され、熱流が従来の固体冷凍機に比べて増大することを明らかにした。また、超伝導単一電子素子の電子輸送に対する非平衡熱準粒子の影響についても研究を行った。さらに、トポロジカル超伝導体等の様々なトポロジカル性についても理論的に研究を行った。
日本学術振興会, 基盤研究(B), 国立研究開発法人産業技術総合研究所, 15H03525

対称性の破れた凝縮系におけるトポロジカル量子現象の総括
科学研究費助成事業
2010年04月01日 - 2016年03月31日
前野 悦輝, 田仲 由喜夫, 石川 修六, 鄭 国慶, 柏谷 聡, 浅野 泰寛, 野村 竜司, 安藤 陽一, 佐藤 昌利, 上田 正仁, 野村 竜司, 佐藤 昌利, 田仲 由喜夫, 浅野 泰寛, 上田 正仁
平成27年度は研究成果とりまとめにあたり、主に次の二点を行った。


第一に、領域活動によるこれまでの研究成果を事後評価報告書にまとめ上げ、文科省でのヒアリングを経て事後評価を受けた。結果は評価A+をいただいた。総合所見において、「本研究領域は世界をリードする多くの研究成果を生み出し、当該学問分野における我が国の国際的優位性の確保と、その向上に大きく貢献した。また、積極的にアウトリーチ活動が実施されたことは、物性物理学における新しい概念の普及という点で高く評価できる。本研究領域の活動によって、多くの若手研究者が育成されたと認められる。」との評価をいただいた。報告書作成に際しては、領域メンバーからの成果情報を収集・集積して、発表論文、招待講演、受賞などに含まれる研究成果内容の分析を加えたうえで、今後の展望も含めた。また、新学術プロジェクトならではの、異なる専門分野研究者間の連携による研究成果・論文成果、5回開催(そのうち2回は国際会議として開催)した領域研究会の成果、17回開催した「集中連携研究会」の成果、若手育成のための若手国際会議や若手相互滞在プログラムの成果、市民講座や出前講義の成果の分析も行った。


第二に、本領域の研究活動から生み出されたトポロジカル量子現象に関する新学術領域をさらに発展させるための活動を行った。まず、引き続き領域のHP と事務局を維持し、研究成果情報の収集と公開に務めるとともに、トポロジカル量子現象の研究に関わる研究者に対しての情報ソース・フォーラムとしての機能も果たし続けた。幸い、後継新学術領域プロジェクト「トポロジーが紡ぐトポロジカル物質科学のフロンティア」が採択されたので、さらに飛躍的な発展を生むために必要な引き継ぎ活動を行った。
日本学術振興会, 新学術領域研究(研究領域提案型), 京都大学, 22103001

トポロジカル超伝導体の常磁性マイスナー現象
科学研究費補助金(基盤研究(B))
2014年 - 2016年
浅野 泰寛
完全反磁性(マイスナー効果）は超伝導体の最も基本的な性質である。ところが超伝導体を小さくすると、常磁性を示す超伝導物質群が存在する。この常磁性マイスナー効果は幾つかの実験があるにもかかわらず、その発現機構は謎のままであった。本研究で我々は、異方的超伝導体（トポロジカル超伝導体）の表面には奇周波数クーパー対と呼ばれる特殊なクーパー対が現れること、また奇周波数クーパー対のために小さな異方的超伝導体は低温において常磁性を示す事を明らかにした。
文部科学省, 基盤研究(B), 北海道大学, 研究代表者, 競争的資金, 26287069

時間反転対称性を破る超伝導体の新奇界面現象
科学研究費補助金(新学術領域研究(研究領域提案型))
2010年 - 2015年
前野 悦輝, 柏谷 聡, 赤崎 達志, 浅野 泰寛
時間反転対称性を破る超伝導体でのトポロジカル量子現象、特にその新奇界面現象について、ルテニウム酸化物Sr2RuO4、および、従来型超伝導体・強磁性体のハイブリッド構造で研究を進めた。
そして、スピン三重項超伝導ならではの半整数磁束量子を観測し、軌道部分の時間反転対称性が破れた「カイラル超伝導」特有の界面状態も観測した。また、超伝導一次相転移など、超伝導対称性の完全理解のための重要事実を積み上げた。さらにトポロジカル超伝導に特有の奇周波数状態の理論を深めて、微小試料で観測する提案を行った。また、奇周波数超伝導の舞台であるSr2RuO4と強磁性薄膜接合系の作製にも成功した。
文部科学省, 新学術領域研究(研究領域提案型), 京都大学, 研究分担者, 競争的資金, 22103002

超伝導クーパー対発光の理論
科学研究費補助金(基盤研究(C))
2010年 - 2012年
浅野 泰寛
発光ダイオード(LED)は交通信号や懐中電灯に使われるなど日々の営みに深く浸透し、省エネルギーの達成と快適な生活の維持を両立させる優れた電子素子である。半導体pn接合で生じる発光という物理現象は、このように極めて身近なものである。最近、発光現象の新たな側面に注目した研究が精力的に行われている。超伝導体を用いたLEDには量子情報操作に不可欠な量子力学的にもつれ合った光子のペアを発生出来ると期待されており、超伝導を担う電子対(クーパー対)がどのような過程で、量子力学的にもつれ合った光子ペアを生成するかを明らかにするのが本研究の目的である。2009年に申請者が報告した理論に基づきクーパー対発光の理論を進展させた。時間に依存する摂動理論を用いて接合から発光するフォトン数の長時間平均を理論的に計算する事が出来る、これは発光強度に対応する。これまでのところ、1次の摂動論の範囲では超伝導の効果が極めて小さい事、2次の摂動論を用いて初めてクーパー対の再結合が記述でき、その発光過程から大きな発光強度が説明できそうな事がわかっている。22年度は更に高次の摂動項の大きさを、見積もった結果3次以上の摂動の高次項が無視できることがわかった。この結果は、連携して研究を進めている実験グループによって見いだされた結果を矛盾なく説明する。さらに実験的には、発行寿命が超伝導転移温度以下で急激に減少する事を見いだ...
文部科学省, 基盤研究(C), 北海道大学, 研究代表者, 競争的資金, 22540355

スピン3重項超流体の近接効果
科学研究費補助金(特定領域研究)
2008年 - 2009年
浅野 泰寛
超伝導には通常金属における超伝導(スピン1重項s波超伝導)の他に,銅酸化物高温超伝導(スピン1重項d波)に代表される異方的超伝導がある.超伝導体に普通の非超伝導金属(常伝導体)を接合したとき,超伝導を担うクーパー対が超伝導体から常伝導体へ染み出す現象は近接効果と呼ばれている.我々はこれまで異方的超伝導体の近接効果を調べ,近接効果はその母体となる超伝導の対称性に極めて敏感であるという重要な結論を得ている.異方的超伝導が非局所電流に及ぼす効果を明らかにする事で本研究の当初の目的のひとつである.特にスピン3重項超伝導体から染み出したクーパー対が奇周波数対称性を獲得することは、我々が明らかにした重要な性質である。奇周波数ペアは、超伝導体と強磁性体が接合した場合にも生み出され、その性質が大変注目されている。我々は、超伝導体に張り付けた金属薄膜における表面インピーダンスが超伝導体のスピン対称性に依存して特徴的なふるまいを示すことを明らかにした。また、強磁性絶縁体を超伝導体で挟んだSFS接合では、強磁性絶縁体の長さを1原子層ずつ変化させるごとにπ接合という特殊な状態が実現することを明らかにした。このπ状態と奇周波数ペアの関係は、今後の課題として残されている。
文部科学省, 特定領域研究, 北海道大学, 研究代表者, 競争的資金, 20029001

エキゾチック超伝導接合における近接効果の理論
科学研究費補助金(基盤研究(C))
2007年 - 2008年
浅野 泰寛, 田仲 由喜夫, 田仲 由喜夫
超伝導の対称性は、金属で発現するスピン1重項対称性と、ルテニウム酸化物や重い電子系で有力とされるスピン3重項対称性に大別される。特にスピン3重項超伝導の物理はきわめて興味深く、注目を集めている。我々は、理論的な手法にのっとり超伝導近接効果を調べ、この2種類を明確に区別する新しい実験方法を提案した。
文部科学省, 基盤研究(C), 北海道大学, 研究代表者, 競争的資金, 19540352

スピン3重項超伝導体におけるスピン流の理論的研究
科学研究費補助金(特定領域研究)
2006年 - 2007年
浅野 泰寛, 市岡 優典
本研究課題ではスピン3重項超伝導体に固有の輸送現象の解明を目指している.18年度はその中でもスピン・ジョセフソン効果の基本的な性質の解明と,観測に向けての提案を行った.超スピン流に関する研究はヘリウム3ですでに行われているが,本研究ではスピン3重項超伝導体Sr_2RuO_4を念頭に超スピン流を制御しながら流すための理論的提案を行った.超伝導体中のクーパー対はスピンの外に電荷の自由度をもち,電荷が電磁場とゲージ結合するためスピン流の制御が可能になるという結論を得た.スピン流の基礎的性質の研究とその応用研究は現在磁性体を用いた微小素子においてきわめて盛んに行われており,デバイス応用の可能性も高くなってきた.その意味で超伝導体を用いたスピン流の研究はとても時宜を得たものと考えられる.19年度はT字形状の超伝導体と常伝導体の接合の電気伝導測定から,スピン1重項超伝導体と3重項超伝導体の峻別が可能であることを示した.この目的のためには多くの実験があるが,ルテニウム酸化物をはじめとして多くの3重項超伝導体について,スピン3重項超伝導を否定する意見もないわけではない.こうした状況の下で,超伝導の対称性をはっきりと区別できる方法の提案は,この分野の発展に大きく寄与すると考えられる.
文部科学省, 特定領域研究, 北海道大学, 研究代表者, 競争的資金, 18043001

巨大近接効果ジョセフソン素子の研究
科学研究費助成事業
2005年 - 2006年
小田 研, 伊土 政幸, 桃野 直樹, 丹田 聡, 浅野 泰寛
本研究は、銅酸化物高温超伝導体における巨大近接効果の起源を解明し、これを用いた新規なタイプのジョセブソン接合を作製することを目的とする。巨大近接効果には、高温超伝導体の特異な性質の一つである擬ギャップ状態が深く関わっていると考えられている。そこで本研究では、擬ギャップ状態の起源に関する知見を得るため、走査トンネル顕微鏡(STM)によりビスマス系銅酸化物高温超伝導体(Bi2212)の擬ギャップを詳しく調べた。その結果、特性エネルギーが擬ギャップである電荷秩序の存在が明らかとなり、擬ギャップは電荷秩序の形成によることが示された。また、この電荷秩序は、d波超伝導ギャップのノードから離れた、いわゆるアンチノード領域の電子状態が関わっていて、T_C以下の超伝導状態でも存続し、ノード付近のフェルミ面(フェルミアーク)領域の準粒子によって起こる超伝導(フェルミアーク超伝導)と共存することも明らかにされた。アンチノード領域の準粒子、あるいは、それらの対(インコヒーレントなクーパー対)が電荷秩序を担うと考えられるが、どちらに起因するかは今後明らかにされるべき大変興味深い問題である。さらに、本研究では、クーパー対の電荷秩序、いわゆる"ボソン結晶"が高温超伝導体で実現していると、これが低温で超流動性を示す可能性(固体超流動の可能性)のあることが指摘され、このことと巨大近接効果の起源との関連性が議論された。
これらの成果については、日本物理学会や高温超伝導に関する幾つかの国際会議で既に報告し、また、論文としてPhys. Rev. Lett.誌などに投稿した。
日本学術振興会, 萌芽研究, 北海道大学, 17654062

トポロジカル量子物質の創製と新規量子現象・量子機能素子の研究
科学研究費助成事業
2003年 - 2005年
丹田 聡, 稲垣 克彦, 宇治 進也, 畠中 憲之, 林 正彦, 松山 豊樹, 浅野 泰寛
NbSe_2ナノチューブ、NbSe_2ナノファイバー、TaS_2ナノチューブの合成に成功した。NbSe_2ナノチューブの合成に関しては、化学的気相輸送法をもちいた。特にC_<60>テンプレートを用いることにより径がナノサイズの大きさのものがコントロールよく合成できることを発見した。NbSe_2ナノチューブの径は10nmから100nmのサイズであり長さは1μmである。温度コントロール(720℃から800℃)を精密に行うことにより、最初にナノサイズのNbSe_3の単結晶を作製し(720℃)その後温度を780℃にしばらく設定しそのNbSe_3から脱Se化反応によりNbSe_2のナノファイバー、ナノチューブを合成する。その際NbSe_3のもつナノファイバー性を利用するいわゆる自己テンプレート型製法を確立した。脱Se化反応においては曲率をもって作製されることがわかっており、その過程においてナノチューブが合成されるというメカニズムを解明した。TaS_2ナノチューブに関しては室温にてCDW転移を示していることが透過電子顕微鏡により観測された。CDWに基づく超格子周期の衛星反射の観測がみられ、かなり薄い結晶においてもCDWが存在することが明らかとなった。NbSe_2ナノファイバー、ナノチューブに4端子電極をつけ転移温度を測定した。電極に関してはFIBによる電極直接接合法と電子ビーム露光法を用いた。Tcは5.0Kでありバルクで報告されているTc=7.2Kより低い温度で超伝導になることがわかった。これらの結果はいずれも世界初の結果である。
日本学術振興会, 基盤研究(A), 北海道大学, 15204029

ナノ電気機械効果による半導体量子ドットにおける新たなブロッケード機構の理論研究
科学研究費助成事業
2003年 - 2004年
西口 規彦, 浅野 泰寛
橋梁構造の力学的な不安定性と、その上に作製された単電子トランジスタとの相互作用による新たな電子輸送に関するブロッケード現象を理論により明らかにし、その現象を考慮した電気伝導特性を導いた。具体的には以下の通りである。:ソース・ドレインおよび量子ドットと基盤間に加えられたゲート電圧により、橋梁部分に静電力が働き基盤方向へたわむ。この構造の変化がゲートキャパシタンスの増加を生じさせ、電子の伝導特性を変化させる。ゲート電圧をさらに増加させると、静電力と均衡を保っていた弾性的な復元力が限界に達し、力学的な不安定性が生じる。この臨界電圧を超えると橋梁部分は突然に基盤へ落下する。両者の間に電荷の移動がなければ、両者は印加電圧が解放されるまで静電力により、くっついた状態が維持される。この臨界状態の近傍では、構造の柔軟性は著しく低下し、外力に対し過敏に応答する。トンネル伝導により量子ドット上の電子数が変化すると、それに応じて量子ドットに働く静電力は不連続に変化する。構造不安定臨界電圧近傍では、この微小な静電力の変化により、橋梁部分が大きく変位する。そのため、量子ドットの基盤からの平衡距離は余剰電子数に依存して不連続に減少し、量子ドットと基盤間の静電容量を増加させる。量子ドットの電子輸送特性は、量子ドットとソース電極、ドレイン電極およびゲート電極間との静電容量によって決定されるため、量子ドット・ゲート電極間の静電容量の変化は電子のトンネル条件を変えることとなる。すなわち、ソースまたはドレインと量子ドット間のトンネル透過の生じるソース・ドレイン電圧とゲート電圧に関する条件が、電子がソース電極から量子ドットに入ってくる場合と、その電子がドレイン電極へ出て行く場合とで異なることになる。オーソドックス理論から予備的な計算をすると、電子がトンネル効果でソースから量子ドットへトンネルした後、構造変形のためドット内の化学ポテンシャルが低下し、ドレインへのトンネル透過の条件が満足されなくなることがソース・ドレイン間の電位差が小さい場合に生じることが判った。また、先に量子ドットからドレインへ電子がトンネルした後に、構造変形のため量子ドット内の化学ポテンシャルが増加しトンネル透過に対して新たなバリアーとして働くことが判った。これらの解析から、トンネル透過の条件の変化はソース・ドレイン間の電位差が小さい場合、すなわちゼロバイアス近傍の電気伝導特性に著しい効果を及ぼすことが判った。ソース・ドレイン間の電位差が小さい場合、コンダクタンスはゼロとなり、構造の変形が新たなブロッケード現象を引き起こすと期待される。
日本学術振興会, 基盤研究(C), 北海道大学, 15510109