Updated on 2024/04/05

写真a

 
KONTANI, Hiroshi
 
Organization
Graduate School of Science Professor
Graduate School
Graduate School of Science
Undergraduate School
School of Science
Title
Professor

Degree 1

  1. Ph. D ( 1996.3   Kyoto University ) 

Research Interests 9

  1. フェルミ液体理論、バーテックス補正

  2. 量子輸送現象

  3. 超伝導発現機構

  4. 電子ネマティック秩序

  5. 鉄系超伝導体

  6. 銅酸化物高温超伝導体

  7. 高温超伝導現象

  8. 強相関電子系の理論

  9. 物性理論

Research Areas 2

  1. Others / Others  / condensed matter physics

  2. Others / Others  / Physical Properties I

Current Research Project and SDGs 4

  1. Theoretical study on the Mechanism of Superconductivity

  2. Transport Phenomena in Strongly Correlated Electron Systems

  3. 強相関超伝導体における電荷・軌道・スピン複合自由度 の協奏現象の理論解明

  4. 鉄系超伝導体の新規な多軌道物理現象と超伝導発現機構

Research History 4

  1. Nagoya University

    2012.4

  2. Nagoya University   Associate professor

    2004.4 - 2012.3

  3. Saitama University   Associate Professor

    2000.10 - 2004.3

  4. The University of Tokyo   Assistant

    1995.4 - 2000.10

Education 3

  1. Kyoto University

    1993.4 - 1995.3

  2. Kyoto University

    1991.4 - 1993.3

  3. Kyoto University

    1987.4 - 1991.3

Professional Memberships 1

  1. 日本物理学会   磁性分科世話人(1998年度)

    1992.3

Committee Memberships 1

  1. 東京大学物性研究所   共同利用施設専門委員会  

    2022.4 - 2024.3   

Awards 2

  1. 久保亮五記念

    2013.9   井上科学振興財団  

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    Country:Japan

  2. 第一回日本物理学会若手奨励賞(2007年)

    2007.6   日本物理学会  

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    Country:Japan

 

Papers 250

  1. Drastic magnetic-field-induced chiral current order and emergent current-bond-field interplay in kagome metals Reviewed

    Rina Tazai, Youichi Yamakawa, Hiroshi Kontani

    Proceedings of the National Academy of Sciences   Vol. 121   page: e2303476121   2024.1

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  2. Charge-loop current order and Z3 nematicity mediated by bond order fluctuations in kagome metals Reviewed

    Tazai, R; Yamakawa, Y; Kontani, H

    NATURE COMMUNICATIONS   Vol. 14 ( 1 )   2023.11

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1038/s41467-023-42952-6

    DOI: 10.1038/s41467-023-42952-6

    Web of Science

    PubMed

  3. Unconventional density waves and superconductivities in Fe-based superconductors and other strongly correlated electron systems Invited Reviewed

    Hiroshi Kontani, Rina Tazai, Youichi Yamakawa, Seiichiro Onari

    Advances in Physics   Vol. 3   page: 355 - 443   2023.1

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: doi.org/10.1080/00018732.2022.2144590

  4. Real-space Loop Current Pattern in Time-reversal-symmetry Breaking Phase in Kagome Metals Reviewed

    Koki Shimura, Rina Tazai, Youichi Yamakawa, Seiichiro Onari, and Hiroshi Kontani

    Journal of the Physical Society of Japan   Vol. 93   page: 033704   2024.2

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: https://doi.org/10.7566/JPSJ.93.033704

    DOI: https://doi.org/10.7566/JPSJ.93.033704

    Other Link: https://journals.jps.jp/doi/10.7566/JPSJ.93.033704

  5. Evidence for an odd-parity nematic phase above the charge-density-wave transition in a kagome metal Reviewed International coauthorship

    T. Asaba, A. Onishi, Y. Kageyama, T. Kiyosue, K. Ohtsuka, S. Suetsugu, Y. Kohsaka, T. Gaggl, Y. Kasahara, H. Murayama, K. Hashimoto, R. Tazai, H. Kontani, B. R. Ortiz, S. D. Wilson, Q. Li, H. -H. Wen, T. Shibauchi, and Y, Matsuda

    Nature Physics   Vol. 20   page: 40 - 46   2024.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: https://doi.org/10.6084/m9.figshare.23557737

    DOI: https://doi.org/10.6084/m9.figshare.23557737

    Other Link: https://www.nature.com/articles/s41567-023-02272-4

  6. Low temperature phase transitions under CDW state in kagome metals AV3Sb5 (A=Cs,Rb,K): Significance of mix-type Fermi surface electron correlations Reviewed

    Jianxin Huang, Rina Tazai, Youichi Yamakawa, Seiichiro Onari, Hiroshi Kontani

    Physical Review B     2024.1

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: https://doi.org/10.1103/PhysRevB.109.L041110

    DOI: https://doi.org/10.1103/PhysRevB.109.L041110

    Other Link: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.109.L041110

  7. Three-dimensional bond-order instability in infinite-layer nickelates due to nonlocal quantum interference Invited Reviewed

    Seiichiro Onari and Hiroshi Kontani

    Physical Review B   Vol. 108   page: L241119   2023.12

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: https://doi.org/10.1103/PhysRevB.108.L241119

    DOI: https://doi.org/10.1103/PhysRevB.108.L241119

    Other Link: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.108.L241119

  8. Rigorous formalism for unconventional symmetry breaking in Fermi liquid theory and its application to nematicity in FeSe Reviewed

    Tazai Rina, Matsubara Shun, Yamakawa Youichi, Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 107 ( 3 )   2023.1

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.107.035137

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  9. Correlation-driven electronic nematicity in the Dirac semimetal BaNiS2 Reviewed

    Butler Christopher John, Kohsaka Yuhki, Yamakawa Youichi, Bahramy Mohammad Saeed, Onari Seiichiro, Kontani Hiroshi, Hanaguri Tetsuo, Shamoto Shinichi

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   Vol. 119 ( 49 )   2022.11

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1073/pnas.2212730119

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  10. Diverse Exotic Orders and Fermiology in Fe-Based Superconductors: A Unified Mechanism for B1g/B2g Nematicity in FeSe/(Cs,Rb)Fe2As2 and Smectic Order in BaFe2As2 Invited Reviewed

    Seiichiro Onari and Hiroshi Kontani

    Frontiers in Physics   Vol. 10   page: 915619   2022.7

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.3389/fphy.2022.915619

  11. Mechanism of exotic density-wave and beyond-Migdal unconventional superconductivity in kagome metal AV(3)Sb(5) (A = K, Rb, Cs) Reviewed

    Tazai Rina, Yamakawa Youichi, Onari Seiichiro, Kontani Hiroshi

    SCIENCE ADVANCES   Vol. 8 ( 13 )   2022.4

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1126/sciadv.abl4108

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  12. SU(4) Valley + Spin Fluctuation Interference Mechanism for Nematic Order in Magic-Angle Twisted Bilayer Graphene: The Impact of Vertex Corrections Reviewed

    Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW LETTERS   Vol. 128 ( 6 )   2022.2

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevLett.128.066401

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  13. d- and p-wave Quantum Liquid Crystal Orders in Cuprate Superconductors, Kappa-(BEDT-TTF)(2)X, and Coupled Chain Hubbard Models: Functional-renormalization-group Analysis Invited Reviewed

    Tazai Rina, Yamakawa Youichi, Tsuchiizu Masahisa, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 90 ( 11 )   2021.11

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.7566/JPSJ.90.111012

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  14. Discovery of mesoscopic nematicity wave in iron-based superconductors Reviewed

    Shimojima T., Motoyui Y., Taniuchi T., Bareille C., Onari S., Kontani H., Nakajima M., Kasahara S., Shibauchi T., Matsuda Y., Shin S.

    SCIENCE   Vol. 373 ( 6559 ) page: 1122 - +   2021.9

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1126/science.abd6701

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  15. Unconventional orbital charge density wave mechanism in the transition metal dichalcogenide 1T-TaS2 Reviewed

    Hirata Toru, Yamakawa Youichi, Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW RESEARCH   Vol. 3 ( 3 )   2021.8

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevResearch.3.L032053

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  16. Pressure-induced reconstitution of Fermi surfaces and spin fluctuations in S-substituted FeSe Reviewed

    Kuwayama T., Matsuura K., Gouchi J., Yamakawa Y., Mizukami Y., Kasahara S., Matsuda Y., Shibauchi T., Kontani H., Uwatoko Y., Fujiwara N.

    SCIENTIFIC REPORTS   Vol. 11 ( 1 )   2021.8

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1038/s41598-021-96277-9

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  17. Generation of odd-frequency surface superconductivity with spontaneous spin current due to the zero-energy Andreev bound state

    Matsubara Shun, Tanaka Yukio, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 103 ( 24 )   2021.6

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.103.245138

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  18. Development of Spin Fluctuations under the Presence of d-wave Bond Order in Cuprate Superconductors

    Ando Satoshi, Yamakawa Youichi, Onari Seiichiro, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 90 ( 6 )   2021.6

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.7566/JPSJ.90.063704

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  19. Prediction of pseudogap formation due to d-wave bond-order in organic superconductor kappa-(BEDT-TTF)(2)X

    Tazai Rina, Yamakawa Youichi, Tsuchiizu Masahisa, Kontani Hiroshi

    PHYSICAL REVIEW RESEARCH   Vol. 3 ( 2 )   2021.5

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevResearch.3.L022014

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  20. Emergence of charge loop current in the geometrically frustrated Hubbard model: A functional renormalization group study

    Tazai Rina, Yamakawa Youichi, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 103 ( 16 )   2021.4

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.103.L161112

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  21. Odd-parity spin-loop-current order mediated by transverse spin fluctuations in cuprates and related electron systems

    Kontani Hiroshi, Yamakawa Youichi, Tazai Rina, Onari Seiichiro

    PHYSICAL REVIEW RESEARCH   Vol. 3 ( 1 )   2021.2

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    DOI: 10.1103/PhysRevResearch.3.013127

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  22. Spin-fluctuation-driven B-1g and B-2g Bond Order and Induced In-plane Anisotropy in Magnetic Susceptibility in Cuprate Superconductors: Impact of Hot-/Cold-spot Structure on Bond-order Symmetry

    Kawaguchi Kouki, Onari Seiichiro, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 89 ( 12 )   2020.12

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.7566/JPSJ.89.124704

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  23. Hidden antiferronematic order in Fe-based superconductor BaFe2As2 and NaFeAs above T-S

    Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW RESEARCH   Vol. 2 ( 4 )   2020.10

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevResearch.2.042005

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  24. Non-Fermi liquid transport in the vicinity of the nematic quantum critical point of superconducting FeSe1-xSx

    Huang W. K., Hosoi S., Culo M., Kasahara S., Sato Y., Matsuura K., Mizukami Y., Berben M., Hussey N. E., Kontani H., Shibauchi T., Matsuda Y.

    PHYSICAL REVIEW RESEARCH   Vol. 2 ( 3 )   2020.9

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevResearch.2.033367

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  25. Doping effects on electronic states in electron-doped FeSe: Impact of self-energy and vertex corrections

    Yamakawa Youichi, Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 102 ( 8 )   2020.8

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.102.081108

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  26. Emergence of d +/- ip-wave superconducting state at the edge of d-wave superconductors mediated by ferromagnetic fluctuations driven by Andreev bound states

    Matsubara Shun, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 101 ( 23 )   2020.6

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.101.235103

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  27. Emergence of strongly correlated electronic states driven by the Andreev bound state in d-wave superconductors

    Matsubara Shun, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 101 ( 7 )   2020.2

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.101.075114

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  28. Multipole fluctuation theory for heavy fermion systems: Application to multipole orders in CeB6

    Tazai Rina, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 100 ( 24 )   2019.12

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.100.241103

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  29. Origin of diverse nematic orders in Fe-based superconductors: 45 degrees rotated nematicity in AFe(2)As(2) (A=Cs, Rb)

    Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 100 ( 2 )   2019.7

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.100.020507

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  30. Hexadecapole Fluctuation Mechanism for s-wave Heavy Fermion Superconductor CeCu2Si2: Interplay between Intra- and Inter-Orbital Cooper Pairs

    Tazai Rina, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 88 ( 6 )   2019.6

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.7566/JPSJ.88.063701

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  31. Pressure-induced quantum critical point in the heavily hydrogen-doped iron-based superconductor LaFeAsO

    Takeuchi Masayoshi, Fujiwara Naoki, Kuwayama Takanori, Nakagawa Satoshi, Iimura Soshi, Matsuishi Satoru, Yamakawa Youichi, Kontani Hiroshi, Hosono Hideo

    PHYSICAL REVIEW B   Vol. 99 ( 17 )   2019.5

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.99.174517

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  32. Fully gapped s-wave superconductivity enhanced by magnetic criticality in heavy-fermion systems

    Tazai Rina, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 98 ( 20 )   2018.11

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.98.205107

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  33. Self-energy driven resonancelike inelastic neutron spectrum in the s(++)-wave state in Fe-based superconductors

    Takeuchi Lisa, Yamakawa Youichi, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 98 ( 16 )   2018.10

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.98.165143

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  34. Pairing mechanism for nodal s-wave superconductivity in BaFe2(As, P)(2): Analysis beyond Migdal-Eliashberg formalism

    Nakaoka Hironori, Yamakawa Youichi, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 98 ( 12 )   2018.9

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.98.125107

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  35. Edge-induced Strongly Correlated Electronic States in Two-dimensional Hubbard Model: Enhancement of Magnetic Correlations and Self-energy Effects

    Matsubara Shun, Yamakawa Youichi, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 87 ( 7 )   2018.7

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.7566/JPSJ.87.073705

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  36. Multistage electronic nematic transitions in cuprate superconductors: A functional-renormalization-group analysis

    Tsuchiizu Masahisa, Kawaguchi Kouki, Yamakawa Youichi, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 97 ( 16 )   2018.4

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.97.165131

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  37. Abrupt change of the superconducting gap structure at the nematic critical point in FeSe1-xSx

    Sato Yuki, Kasahara Shigeru, Taniguchi Tomoya, Xing Xiangzhuo, Kasahara Yuichi, Tokiwa Yoshifumi, Yamakawa Youichi, Kontani Hiroshi, Shibauchi Takasada, Matsuda Yuji

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   Vol. 115 ( 6 ) page: 1227-1231   2018.2

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1073/pnas.1717331115

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  38. Nematicity, magnetism, and superconductivity in FeSe under pressure: Unified explanation based on the self-consistent vertex correction theory

    Youichi Yamakawa, Hiroshi Kontani

    Phys. Rev. B   Vol. 96 ( 14 ) page: 144509   2017.10

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.96.144509

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  39. In-plane anisotropy of transport coefficients in electronic nematic states: Universal origin of nematicity in Fe-based superconductors

    Phys. Rev. B   Vol. 96 ( 9 ) page: 094527   2017.9

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    DOI: 10.1103/PhysRevB.96.094527

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  40. Superconductivity without a hole pocket in electron-doped FeSe: Analysis beyond the Migdal-Eliashberg formalism

    Phys. Rev. B   Vol. 96 ( 4 ) page: 043130   2017.7

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.96.045130

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  41. Plain s-Wave Superconductivity near Magnetic Criticality: Enhancement of Attractive Electron-Boson Coupling Vertex Corrections

    Tazai Rina, Yamakawa Youichi, Tsuchiizu Masahisa, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 86 ( 7 )   2017.7

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.7566/JPSJ.86.073703

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  42. Competing Unconventional Charge-Density-Wave States in Cuprate Superconductors: Spin-Fluctuation-Driven Mechanism

    Kawaguchi Kouki, Yamakawa Youichi, Tsuchiizu Masahisa, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 86 ( 6 )   2017.6

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    DOI: 10.7566/JPSJ.86.063707

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  43. High-Tc Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

    Phys. Rev. Lett.   Vol. 118 ( 14 ) page: 147004   2017.4

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    DOI: 10.1103/PhysRevLett.118.147004

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  44. Unusual nodal behaviors of the superconducting gap in the iron-based superconductor Ba(Fe0.65Ru0.35)(2)As-2: Effects of spin-orbit coupling

    Liu L., Okazaki K., Yoshida T., Suzuki H., Horio M., Ambolode L. C. C. II, Xu J., Ideta S., Hashimoto M., Lu D. H., Shen Z. -X., Ota Y., Shin S., Nakajima M., Ishida S., Kihou K., Lee C. H., Iyo A., Eisaki H., Mikami T., Kakeshita T., Yamakawa Y., Kontani H., Uchida S., Fujimori A.

    PHYSICAL REVIEW B   Vol. 95 ( 10 )   2017.3

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.95.104504

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  45. Functional renormalization group study of orbital fluctuation mediated superconductivity: Impact of the electron-boson coupling vertex corrections

    Rina Tazai, Youichi Yamakawa, Masahisa Tsuchiizu, Hiroshi Kontani

    Physical Review B   Vol. 94 ( 11 ) page: 115155   2016.9

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.94.115155

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  46. Theoretical prediction of nematic orbital-ordered state in the Ti oxypnictide superconductor BaTi2(As,Sb)(2)O

    Nakaoka Hironori, Yamakawa Youichi, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 93 ( 24 )   2016.6

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.93.245122

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  47. Nematicity and magnetism in FeSe and other families of Fe-based superconductors

    Youichi Yamakawa, Seiichiro Onari, Hiroshi Kontani

    Physical Review X   Vol. 6 ( 2 ) page: 021032   2016.6

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevX.6.021032

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  48. Sign-reversing orbital polarization in the nematic phase of FeSe due to the $C_2$ symmetry-breaking in the self-energy

    Seiichiro Onari, Youichi Yamakawa, Hiroshi Kontani

    Physical Review Letters   Vol. 116 ( 22 ) page: 227001   2016.6

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevLett.116.227001

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  49. p-orbital density wave with d symmetry in high-T-c cuprate superconductors predicted by renormalization-group plus constrained RPA theory

    Tsuchiizu Masahisa, Yamakawa Youichi, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 93 ( 15 )   2016.4

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.93.155148

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  50. Superconductivity pairing mechanism from cobalt impurity doping in FeSe: Spin (s(+/-)) or orbital (s(++)) fluctuation

    Urata T., Tanabe Y., Huynh K. K., Yamakawa Y., Kontani H., Tanigaki K.

    PHYSICAL REVIEW B   Vol. 93 ( 1 )   2016.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.93.014507

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  51. Momentum-dependent sign inversion of orbital order in superconducting FeSe

    Suzuki Y., Shimojima T., Sonobe T., Nakamura A., Sakano M., Tsuji H., Omachi J., Yoshioka K., Kuwata-Gonokami M., Watashige T., Kobayashi R., Kasahara S., Shibauchi T., Matsuda Y., Yamakawa Y., Kontani H., Ishizaka K.

    PHYSICAL REVIEW B   Vol. 92 ( 20 )   2015.11

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.92.205117

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  52. Revisiting orbital-fluctuation-mediated superconductivity in LiFeAs: Nontrivial spin-orbit interaction effects on the band structure and superconducting gap function

    Saito Tetsuro, Yamakawa Youichi, Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 92 ( 13 )   2015.10

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.92.134522

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  53. $p$-orbital density wave with $d$ symmetry in high-$T_c$ cuprate superconductors predicted by the renormalization-group + constrained RPA theory Reviewed

    Masahisa Tsuchiizu, Youichi Yamakawa, Hiroshi Kontani

    Physical Review B   Vol. 93   page: 155148   2015.7

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.92.045124

  54. Quasiparticle Interference in Fe-based Superconductors Based on a Five-Orbital Tight-Binding Model Reviewed

    Youichi Yamakawa, Hiroshi Kontani

    Physical Review B   Vol. 92   page: 045124   2015.6

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    DOI: 10.1103/PhysRevB.92.045124

  55. Spin-Fluctuation-Driven Nematic Charge-Density Wave in Cuprate Superconductors: Impact of Aslamazov-Larkin Vertex Corrections

    Youichi Yamakawa and Hiroshi Kontani

    Physical Review Letters   Vol. 114 ( 25 ) page: 257001   2015.6

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    DOI: 10.1103/PhysRevLett.114.257001

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  56. Spin-triplet superconductivity in Sr2RuO4 due to orbital and spin fluctuations: Analyses by two-dimensional renormalization group theory and self-consistent vertex-correction method

    Masahisa Tsuchiizu, Youichi Yamakawa, Seiichiro Onari, Yusuke Ohno, and Hiroshi Kontani

    Physical Review B   Vol. 91 ( 15 ) page: 2015   2015.4

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    DOI: 10.1103/PhysRevB.91.155103

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  57. Quantum critical behavior in heavily doped LaFeAsO$_{1-x}$H$_x$ pnictide superconductors analyzed using nuclear magnetic resonance

    R. Sakurai, N. Fujiwara, N. Kawaguchi, Y. Yamakawa, H. Kontani, S. Iimura, S. Matsuishi, H. Hosono

    Physical Review B   Vol. 91 ( 6 ) page: 064509   2015.2

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    DOI: 10.1103/PhysRevB.91.064509

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  58. Orbital plus Spin Multimode Fluctuation Theory in Iron-based Superconductors

    Onari Seiichiro, Kontani Hiroshi

    IRON-BASED SUPERCONDUCTIVITY   Vol. 211   page: 331-376   2015

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    DOI: 10.1007/978-3-319-11254-1_9

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  59. Anisotropy of the superconducting gap in the iron-based superconductor BaFe2(As1-xPx)(2)

    Yoshida T., Ideta S., Shimojima T., Malaeb W., Shinada K., Suzuki H., Nishi I., Fujimori A., Ishizaka K., Shin S., Nakashima Y., Anzai H., Arita M., Ino A., Namatame H., Taniguchi M., Kumigashira H., Ono K., Kasahara S., Shibauchi T., Terashima T., Matsuda Y., Nakajima M., Uchida S., Tomioka Y., Ito T., Kihou K., Lee C. H., Iyo A., Eisaki H., Ikeda H., Arita R., Saito T., Onari S., Kontani H.

    SCIENTIFIC REPORTS   Vol. 4   2014.12

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    DOI: 10.1038/srep07292

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  60. Linear Response Theory for Shear Modulus $C_{66}$ and Raman Quadrupole Susceptibility: Significant Evidence for Orbital Nematic Fluctuations in Fe-Based Superconductors

    Hiroshi Kontani, and Youichi Yamakawa

    Phys. Rev. Lett.   Vol. 113 ( 4 ) page: 047001 (5p)   2014.7

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    DOI: 10.1103/PhysRevLett.113.047001

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  61. Reproduction of experimental gap structure in LiFeAs based on orbital-spin fluctuation theory: s(++)-wave, s(+/-)-wave, and hole-s(+/-)-wave states

    Saito Tetsuro, Onari Seiichiro, Yamakawa Youichi, Kontani Hiroshi, Borisenko Sergey V., Zabolotnyy Volodymyr B.

    PHYSICAL REVIEW B   Vol. 90 ( 3 )   2014.7

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    DOI: 10.1103/PhysRevB.90.035104

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  62. High-Tc Superconductivity near the Anion Height Instability in Fe-Based Superconductors

    Seiichiro Onari, Youichi Yamakawa, and Hiroshi Kontani

    Phys. Rev. Lett.   Vol. 112 ( 18 ) page: 187001 (5p)   2014.5

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    DOI: 10.1103/PhysRevLett.112.187001

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  63. NMR Study on a Pnictide Superconductor LaFeAsO1-x H (x) in a H-Overdoped Regime: Revival of Antiferromagnetic Fluctuations

    Fujiwara N., Iimura S., Matsuishi S., Hosono H., Yamakawa Y., Kontani H.

    JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM   Vol. 27 ( 4 ) page: 933-936   2014.4

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    DOI: 10.1007/s10948-013-2413-z

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  64. Microstructural Analysis of Low-cycle Fatigue Damage Process of Sn-Ag-Cu Solder Joint

    Kontani Hiroyuki, Kariya Yoshiharu, Fumikura Tomoya

    PROCEEDINGS OF THE ASME INTERNATIONAL TECHNICAL CONFERENCE AND EXHIBITION ON PACKAGING AND INTEGRATION OF ELECTRONIC AND PHOTONIC MICROSYSTEMS, 2013, VOL 1     2014

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  65. Infrared anomalous Hall effect in CaxSr1-xRuO3 films

    Kim M. -H., Tanaka T., Ellis C. T., Mukherjee A., Acbas G., Ohkubo I., Christen H., Mandrus D., Kontani H., Cerne J.

    PHYSICAL REVIEW B   Vol. 88 ( 15 )   2013.10

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    DOI: 10.1103/PhysRevB.88.155101

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  66. Orbital Nematic Instability in Two-Orbital Hubbard Model: Renormalization-Group + Constrained RPA Analysis Reviewed

    Yusuke Ohno, Masahisa Tsuchiizu, Seiichiro Onari, Hiroshi Kontani

    Physical Review Letters   Vol. 111   page: 057003   2013.9

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    Motivated by the nematic electronic fluid phase in Sr_{3}Ru_{2}O_{7}, we develop a combined scheme of the renormalization-group method and the random-phase-approximation-type method, and analyze orbital susceptibilities of the (d_{xz},d_{yz})-orbital Hubbard model with high accuracy. It is confirmed that the present model exhibits a ferro-orbital instability near the magnetic or superconducting quantum criticality, due to the Aslamazov-Larkin-type vertex corrections. This mechanism of orbital nematic order presents a natural explanation for the nematic order in Sr_{3}Ru_{2}O_{7}, and is expected to be realized in various multiorbital systems, such as Fe-based superconductors.

  67. Zigzag Chain Structure Transition and Orbital Fluctuations in Ni-Based Superconductors

    Yamakawa Youichi, Onari Seiichiro, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 82 ( 9 )   2013.9

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    DOI: 10.7566/JPSJ.82.094704

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  68. Detection of antiferromagnetic ordering in heavily doped LaFeAsO1-xHx pnictide superconductors using nuclear-magnetic-resonance techniques

    N. Fujiwara, S. Tsutsumi, S. Iimura, S. Matsuishi, H. Hosono, Y. Yamakawa, and H. Kontani

    Phys. Rev. Lett.   Vol. 111 ( 9 ) page: 097002 (4p)   2013.8

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    DOI: 10.1103/PhysRevLett.111.097002

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  69. Orbital Nematic Instability in Two-Orbital Hubbard Model: Renormalization-Group + Constrained RPA Analysis

    Masahisa Tsuchiizu, Yusuke Ohno, Seiichiro Onari, Hiroshi Kontani

    Physical Review Letters   Vol. 111 ( 5 ) page: 057003   2013.7

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    DOI: 10.1103/PhysRevLett.111.057003

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  70. Phase diagram and superconducting states in LaFeAsO1-xHx based on the multiorbital extended Hubbard model

    Yamakawa Y., Onari S., Kontani H., Fujiwara N., Iimura S., Hosono H.

    PHYSICAL REVIEW B   Vol. 88 ( 4 )   2013.7

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    DOI: 10.1103/PhysRevB.88.041106

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  71. Nodal gap structure in Fe-based superconductors due to the competition between orbital and spin fluctuations

    Saito Tetsuro, Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 88 ( 4 )   2013.7

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    DOI: 10.1103/PhysRevB.88.045115

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  72. Effect of realistic finite-size impurities on T-c in Fe-based superconductors based on the five-orbital tight-binding model

    Yamakawa Youichi, Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 87 ( 19 )   2013.5

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    DOI: 10.1103/PhysRevB.87.195121

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  73. Spin-Fluctuation-Driven Orbital Nematic Order in Ru-Oxides: Self-Consistent Vertex Correction Analysis for Two-Orbital Model

    Ohno Yusuke, Tsuchiizu Masahisa, Onari Seiichiro, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 82 ( 1 )   2013.1

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    DOI: 10.7566/JPSJ.82.013707

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  74. Extrinsic Spin Hall Effect Due to Transition-Metal Impurities

    Tanaka Takuro, Kontani Hiroshi

    PROGRESS OF THEORETICAL PHYSICS   Vol. 128 ( 5 ) page: 805-828   2012.11

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  75. Self-consistent Vertex Correction Analysis for Iron-based Superconductors: Mechanism of Coulomb Interaction-Driven Orbital Fluctuations

    Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW LETTERS   Vol. 109 ( 13 )   2012.9

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    DOI: 10.1103/PhysRevLett.109.137001

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  76. Spin Hall effect in iron-based superconductors: A Dirac-point effect

    Pandey Sudhakar, Kontani Hiroshi, Hirashima Dai S., Arita Ryotaro, Aoki Hideo

    PHYSICAL REVIEW B   Vol. 86 ( 6 )   2012.8

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    DOI: 10.1103/PhysRevB.86.060507

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  77. Effect of inelastic scattering on the nuclear magnetic relaxation rate 1/T1T in iron-based superconductors

    Yamakawa Youichi, Onari Seiichiro, Kontani Hiroshi

    SUPERCONDUCTOR SCIENCE & TECHNOLOGY   Vol. 25 ( 8 )   2012.8

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    DOI: 10.1088/0953-2048/25/8/084006

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  78. Superconductivity suppression of Ba(0.5)K(0.5)Fe2-2xM2xAs(2) single crystals by substitution of transition metal (M = Mn, Ru, Co, Ni, Cu, and Zn)

    Li J., Guo Y. F., Zhang S. B., Yuan J., Tsujimoto Y., Wang X., Sathish C. I., Sun Y., Yu S., Yi W., Yamaura K., Takayama-Muromachiu E., Shirako Y., Akaogi M., Kontani H.

    PHYSICAL REVIEW B   Vol. 85 ( 21 )   2012.6

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    DOI: 10.1103/PhysRevB.85.214509

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  79. Impurity-induced electronic nematic state and C-2-symmetric nanostructures in iron pnictide superconductors

    Inoue Yoshio, Yamakawa Youichi, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 85 ( 22 )   2012.6

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    DOI: 10.1103/PhysRevB.85.224506

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  80. Self-consistent Vertex Correction Analysis for Iron-based Superconductors: Mechanism of Coulomb Interaction-Driven Orbital Fluctuations Reviewed

    S. Onari and H. Kontani

    Phys. Rev. Lett.   Vol. 109   page: 137001   2012.6

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    We study the mechanism of orbital/spin fluctuations due to multiorbital Coulomb interaction in iron-based superconductors, going beyond the random-phase-approximation. For this purpose, we develop a self-consistent vertex correction (SC-VC) method, and find that multiple orbital fluctuations in addition to spin fluctuations are mutually emphasized by the "multimode interference effect" described by the VC. Then, both the antiferro-orbital and ferro-orbital (=nematic) fluctuations simultaneously develop for $J/U \sim 0.1$, both of which contribute to the s-wave superconductivity. Especially, the ferro-orbital fluctuations give the orthorhombic structure transition as well as the softening of shear modulus $C_{66}$.

  81. Non-Fermi-liquid transport phenomena and superconductivity driven by orbital fluctuations in iron pnictides: Analysis by fluctuation-exchange approximation

    Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 85 ( 13 )   2012.4

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    DOI: 10.1103/PhysRevB.85.134507

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  82. Orbital fluctuation theory in iron-based superconductors: s++-wave superconductivity, structure transition, and impurity-induced nematic order Invited Reviewed

    H. Kontani, I. Yoshio. T. Saito, Y. Yamakawa and S. Onari

    Solid State Communications   Vol. 152   page: 718-727   2012.4

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    The main features in iron-based superconductors would be (i) the orthorhombic transition accompanied by remarkable softening of shear modulus, (ii) high-Tc superconductivity close to the orthorhombic phase, and (iii) nematic transition in the tetragonal phase. In this paper, we present a unified explanation for them, based on the orbital fluctuation theory, considering both the e-ph and the Coulomb interaction. It is found that a small e-ph coupling constant ($\lambda ~ 0.2$) is enough to produce large orbital (=charge quadrupole $O_{xz/yz}$) fluctuations, which causes the s-wave superconductivity without sign reversal ($s_{++}$-wave state). The derived orbital fluctuations also cause the instability toward the structure transition due to the bound state formation of two orbitons with opposite momenta, which is called the "two-orbiton process". Moreover, impurity-induced non-local orbital order with $C_2$-symmetry is obtained when the orbital fluctuations are strong. This "impurity-induced nematic state" explains the in-plane anisotropy of resistivity in detwinned samples. We stress that (i)-(iii) are reproducible only when orbital fluctuations with respect to $O_{xz}$ and $O_{yz}$ charge quadrupoles are the most divergent. This fact ensures the reliability of the present model Hamiltonian and calculation.

  83. Orbital fluctuation theory in iron-based superconductors: s(++)-wave superconductivity, structure transition, and impurity-induced nematic order

    Kontani Hiroshi, Inoue Yoshio, Saito Tetsuro, Yamakawa Youichi, Onari Seiichiro

    SOLID STATE COMMUNICATIONS   Vol. 152 ( 8 ) page: 718-727   2012.4

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    DOI: 10.1016/j.ssc.2012.01.012

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  84. Study of non-Fermi-liquid-like state and pairing symmetry in iron pnictides based on the multiorbital Hubbard-Holstein model

    Onari S., Kontani H.

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 471 ( 21-22 ) page: 670-674   2011.11

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    DOI: 10.1016/j.physc.2011.05.023

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  85. Extremely strong-coupling superconductivity in artificial two-dimensional Kondo lattices

    Mizukami Y., Shishido H., Shibauchi T., Shimozawa M., Yasumoto S., Watanabe D., Yamashita M., Ikeda H., Terashima T., Kontani H., Matsuda Y.

    NATURE PHYSICS   Vol. 7 ( 11 ) page: 849 - 853   2011.11

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    DOI: 10.1038/NPHYS2112

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  86. Neutron inelastic scattering peak by dissipationless mechanism in the s(++)-wave state in iron-based superconductors

    Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 84 ( 14 )   2011.10

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    DOI: 10.1103/PhysRevB.84.144518

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  87. Linear decrease of critical temperature with increasing Zn substitution in the iron-based superconductor BaFe1.89-2xZn2xCo0.11As2

    Li Jun, Guo Yanfeng, Zhang Shoubao, Yu Shan, Tsujimoto Yoshihiro, Kontani Hiroshi, Yamaura Kazunari, Takayama-Muromachi Eiji

    PHYSICAL REVIEW B   Vol. 84 ( 2 )   2011.7

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    DOI: 10.1103/PhysRevB.84.020513

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  88. Origin of orthorhombic transition, magnetic transition, and shear-modulus softening in iron pnictide superconductors: Analysis based on the orbital fluctuations theory

    Kontani Hiroshi, Saito Tetsuro, Onari Seiichiro

    PHYSICAL REVIEW B   Vol. 84 ( 2 )   2011.7

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    DOI: 10.1103/PhysRevB.84.024528

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  89. Comment on "Violation of Anderson's Theorem for the Sign-Reversing s-Wave State of Iron-Pnictide Superconductors" Reply

    Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW LETTERS   Vol. 106 ( 25 )   2011.6

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    DOI: 10.1103/PhysRevLett.106.259702

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  90. Indication of intrinsic spin Hall effect in 4d and 5d transition metals

    Morota M., Niimi Y., Ohnishi K., Wei D. H., Tanaka T., Kontani H., Kimura T., Otani Y.

    PHYSICAL REVIEW B   Vol. 83 ( 17 )   2011.5

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    DOI: 10.1103/PhysRevB.83.174405

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  91. Comment on "Orbital Order, Structural Transition and Superconductivity in Iron Pnictides" [J. Phys. Soc. Jpn. 79 (2010) 123707]

    Kontani Hiroshi, Onari Seiichiro

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 80 ( 5 )   2011.5

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    DOI: 10.1143/JPSJ.80.056001

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  92. Emergence of fully gapped s(++)-wave and nodal d-wave states mediated by orbital and spin fluctuations in a ten-orbital model of KFe2Se2

    Saito Tetsuro, Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 83 ( 14 )   2011.4

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    DOI: 10.1103/PhysRevB.83.140512

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  93. Emergence of Fully-Gapped s++-wave and Nodal d-wave States Mediated by Orbital- and Spin-Fluctuations in Ten-Orbital Model for KFe2Se2 Reviewed

    T. Saito, S. Onari, and H. Kontani

    Phys. Rev. B   Vol. 83   page: 140512   2011

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  94. Extremely strong-coupling superconductivity in artificial two-dimensional Kondo lattices Reviewed

    Y. Mizukami, H. Shishido, T. Shibauchi, M. Shimozawa, S. Yasumoto, D. Watanabe, M.Yamashita, H. Ikeda, T. Terashima, H. Kontani, and Y. Matsuda

    Nature Physics   Vol. 7   page: 849   2011

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  95. Neutron inelastic scattering peak by dissipationless mechanism in the s++-wave state in iron-based superconductors Reviewed

    S. Onari and H. Kontani

    Phys. Rev. B   Vol. 84   page: 144518   2011

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  96. Linear decrease of critical temperature with increasing Zn substitution in the iron-based superconductor Reviewed

    Jun Li, Y. Guo, S. Zhang, S. Yu, Y. Tsujimoto, H. Kontani, K. Yamaura, and E. Takayama-Muromachi

    Phys. Rev. B   Vol. 84   page: 020513   2011

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  97. Origin of Orthorhombic Transition, Magnetic Transition, and Shear Modulus Softening in Iron Pnictide Superconductors: Analysis based on the Orbital Fluctuation Theory Reviewed

    H. Kontani, T. Saito, and S. Onari

    Phys. Rev. B   Vol. 84   page: 024528   2011

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  98. Indication of intrinsic spin Hall effect in 4d and 5d transition metals Reviewed

    M. Morota, Y. Niimi, K. Ohnishi, T. Tanaka, H. Kontani, T. Kimura, Y. Otani

    Phys. Rev. B   Vol. 83   page: 174405   2011

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  99. Nonmagnetic impurity effects and neutron scattering spectrum in iron pnictides

    Onari S., Kontani H.

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 470 ( 20 ) page: 1007-1009   2010.11

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    DOI: 10.1016/j.physc.2010.05.021

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  100. Orbital fluctuation theory in iron pnictides: Effects of As-Fe-As bond angle, isotope substitution, and Z(2)-orbital pocket on superconductivity

    Saito Tetsuro, Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 82 ( 14 )   2010.10

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    DOI: 10.1103/PhysRevB.82.144510

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  101. Orbital fluctuation theory in iron pnictides: Effects of As-Fe-As bond angle, isotope substitution, and Z2-orbital pocket on superconductivity Reviewed

    Tetsuro Saito, Seiichiro Onari, Hiroshi Kontani

    Physical Review B   Vol. 82 ( 14 ) page: 144510   2010.10

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    We study the pairing mechanism in iron pnictide superconductors based on the five-orbital Hubbard-Holstein model. Due to Fe-ion oscillations, the s-wave superconducting (SC) state without sign reversal (s++-wave state) is induced by orbital fluctuations by using realistic model parameters. The virtue of the present theory is that the famous empirical relation between Tc and the As-Fe-As bond angle is automatically explained since the electron-phonon coupling that creates the orbital fluctuations is the strongest when the As4 tetrahedron is regular. The negative iron isotope effect is also reproduced. In addition, the magnitude of the SC gap on hole pockets is predicted to be rather insensitive to the corresponding d orbital (xz/yz or z2 orbital), which is consistent with the recent bulk-sensitive angle-resolved photoemission spectroscopy (ARPES) measurement for (Ba,K)Fe2As2 and BaFe2(As,P)2. These obtained results indicate that the orbital fluctuation mediated s++-wave state is a plausible candidate for iron pnictides.

  102. Terahertz Hall measurements on optimally doped single-crystal Bi2Sr2CaCu2O8+x

    Jenkins G. S., Schmadel D. C., Sushkov A. B., Gu G. D., Kontani H., Drew H. D.

    PHYSICAL REVIEW B   Vol. 82 ( 9 )   2010.9

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    DOI: 10.1103/PhysRevB.82.094518

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  103. Anomalous Hall effect due to noncollinearity in pyrochlore compounds: Role of orbital Aharonov-Bohm effect

    Tomizawa Takeshi, Kontani Hirhoshi

    PHYSICAL REVIEW B   Vol. 82 ( 10 )   2010.9

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    DOI: 10.1103/PhysRevB.82.104412

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  104. Anomalous Hall effect due to noncollinearity in pyrochlore compounds: Role of orbital Aharonov-Bohm effect Reviewed

    Takeshi Tomizawa, Hirhoshi Kontani

    physical Review B   Vol. 82 ( 10 ) page: 104412   2010.9

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    To elucidate the origin of spin structure-driven anomalous Hall effect (AHE) in pyrochlore compounds, we construct the t2g-orbital kagome lattice model and analyze the anomalous Hall conductivity (AHC). We reveal that a conduction electron acquires a Berry phase due to the complex d-orbital wave function in the presence of spin-orbit interaction. This orbital Aharonov-Bohm (AB) effect produces the AHC that is drastically changed in the presence of noncollinear spin structure. In both ferromagnetic compound Nd2Mo2O7 and paramagnetic compound Pr2Ir2O7, the AHC given by the orbital AB effect totally dominates the spin-chirality mechanism and succeeds in explaining the experimental relation between the spin structure and the AHC.

  105. Intrinsic spin and orbital Hall effects in heavy-fermion systems

    Tanaka T., Kontani H.

    PHYSICAL REVIEW B   Vol. 81 ( 22 )   2010.6

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    DOI: 10.1103/PhysRevB.81.224401

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  106. Tight-binding study of anomalous Hall effect in ferromagnetic 3d transition metals

    Naito T., Hirashima D. S., Kontani H.

    PHYSICAL REVIEW B   Vol. 81 ( 19 )   2010.5

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    DOI: 10.1103/PhysRevB.81.195111

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  107. Orbital-Fluctuation-Mediated Superconductivity in Iron Pnictides: Analysis of the Five-Orbital Hubbard-Holstein Model

    Kontani Hiroshi, Onari Seiichiro

    PHYSICAL REVIEW LETTERS   Vol. 104 ( 15 )   2010.4

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    DOI: 10.1103/PhysRevLett.104.157001

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  108. Orbital-Fluctuation-Mediated Superconductivity in Iron Pnictides: Analysis of the Five-Orbital Hubbard-Holstein Model Reviewed

    Hiroshi Kontani, Seiichiro Onari

    Physical Review Letters   Vol. 104 ( 15 ) page: 157001   2010.4

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    In iron pnictides, we find that the moderate electron-phonon interaction due to the Fe-ion oscillation can induce the critical d-orbital fluctuations, without being prohibited by the Coulomb interaction. These fluctuations give rise to the strong pairing interaction for the s-wave superconducting (SC) state without sign reversal (s++-wave state), which is consistent with experimentally observed robustness of superconductivity against impurities. When the magnetic fluctuations due to Coulomb interaction are also strong, the SC state shows a smooth crossover from the s-wave state with sign reversal (s±-wave state) to the s++-wave state as impurity concentration increases.

  109. Tuning the Dimensionality of the Heavy Fermion Compound CeIn3

    Shishido H., Shibauchi T., Yasu K., Kato T., Kontani H., Terashima T., Matsuda Y.

    SCIENCE   Vol. 327 ( 5968 ) page: 980-983   2010.2

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    DOI: 10.1126/science.1183376

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  110. Structure of Neutron-Scattering Peak in both s++ wave and s+- wave states of an Iron pnictide Superconductor Reviewed

    Seiichiro Onari, Hiroshi Kontani, Masatoshi Sato

    physical Review B   Vol. 81 ( 6 ) page: 060504(R)   2010.2

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    We study the neutron-scattering spectrum in iron pnictides based on the random-phase approximation in the five-orbital model for fully gapped s-wave states with sign reversal (s±) and without sign reversal (s++). In the s++-wave state, we find that a prominent hump structure appears just above the spectral gap by taking account of the quasiparticle damping γ due to strong electron-electron correlation: as the superconductivity develops, the reduction in γ gives rise to the large overshoot in the spectrum above the gap. The obtained hump structure looks similar to the resonance peak in the s±-wave state, although the height and weight of the peak in the latter state is much larger. In the present study, experimentally observed broad spectral peak in iron pnictides is naturally reproduced by assuming the s++-wave state.

  111. Structure of neutron-scattering peaks in both s(++)-wave and s(+/-)-wave states of an iron pnictide superconductor

    Onari Seiichiro, Kontani Hiroshi, Sato Masatoshi

    PHYSICAL REVIEW B   Vol. 81 ( 6 )   2010.2

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    DOI: 10.1103/PhysRevB.81.060504

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  112. Origin of the anomalous Hall effect in the overdoped n-type superconductor Pr(2-x)Ce(x)Cuo(4): Current-vertex corrections due to antiferromagnetic fluctuations

    Jenkins G. S., Schmadel D. C., Bach P. L., Greene R. L., Bechamp-Laganiere X., Roberge G., Fournier P., Kontani Hiroshi, Drew H. D.

    PHYSICAL REVIEW B   Vol. 81 ( 2 )   2010.1

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    DOI: 10.1103/PhysRevB.81.024508

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  113. Violation of Anderson's Theorem for the Sign-Reversing s-Wave State of Iron-Pnictide Superconductors

    Onari Seiichiro, Kontani Hiroshi

    PHYSICAL REVIEW LETTERS   Vol. 103 ( 17 )   2009.10

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    DOI: 10.1103/PhysRevLett.103.177001

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  114. *Violation of Anderson's Theorem for the Sign-Reversing s-Wave State of Iron-Pnictide Superconductors Invited Reviewed

    Seiichiro Onari and Hiroshi Kontani

    Physical Review Letters   Vol. 103   page: 177001   2009.10

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    Based on the five-orbital model, we study the effect of local impurity in iron pnictides, and find that the interband impurity scattering is promoted by the d-orbital degree of freedom. This fact means that the fully gapped sign-reversing s-wave state, which is predicted by spin fluctuation theories, is very fragile against impurities. In the BCS theory, only 1% impurities with intermediate strength induce huge pair breaking, resulting in the large in-gap state and prominent reduction in Tc, contrary to the prediction based on simple orbital-less models. The present study provides a stringent constraint on the pairing symmetry and the electronic states in iron pnictides.

  115. Anomalous Hall effect in the t2g orbital kagome lattice due to noncollinearity: Significance of the orbital Aharonov-Bohm effect Reviewed

    Takeshi Tomizawa and Hiroshi Kontani

    Physical Review B   Vol. 80   page: 100401   2009.9

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    A mechanism of spin structure-driven anomalous Hall effect (AHE) in tilted ferromagnetic metals is proposed by taking account of the d-orbital degree of freedom. We find that a conduction electron acquires a Berry phase due to the complex d-orbital wave function, in the presence of noncollinear spin structure and the spin-orbit interaction. The AHE driven by this orbital-derived Berry phase is much larger than the AHE induced by spin chirality, and it naturally explains the salient features of spin structure-driven AHE in pyrochlore Nd2Mo2O7. Since the proposed AHE can occur even for coplanar spin orders (Mz=0), it is expected to emerge in other interesting geometrically frustrated systems.

  116. Anomalous Hall effect in the t2g orbital kagome lattice due to noncollinearity: Significance of the orbital Aharonov-Bohm effect

    Tomizawa Takeshi, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 80 ( 10 )   2009.9

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    DOI: 10.1103/PhysRevB.80.100401

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  117. Anomalous and spin Hall effects in magnetic granular films

    Inoue Jun-ichiro, Tanaka Takuro, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 80 ( 2 )   2009.7

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    DOI: 10.1103/PhysRevB.80.020405

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  118. Impurity-induced in-gap state and T-c in sign-reversing s-wave superconductors: analysis of iron oxypnictide superconductors

    Senga Yuko, Kontani Hiroshi

    NEW JOURNAL OF PHYSICS   Vol. 11   2009.3

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    DOI: 10.1088/1367-2630/11/3/035005

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  119. Unconventional Pairing Originating from the Disconnected Fermi Surfaces of Superconducting LaFeAsO1-xFx (vol 101, 087004, 2008)

    Kuroki Kazuhiko, Onari Seiichiro, Arita Ryotaro, Usui Hidetomo, Tanaka Yukio, Kontani Hiroshi, Aoki Hideo

    PHYSICAL REVIEW LETTERS   Vol. 102 ( 10 )   2009.3

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    DOI: 10.1103/PhysRevLett.102.109902

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  120. Unconventional pairing originating from disconnected Fermi surfaces in the iron-based superconductor

    Kuroki Kazuhiko, Onari Seiichiro, Arita Ryotaro, Usui Hidetomo, Tanaka Yukio, Kontani Hiroshi, Aoki Hideo

    NEW JOURNAL OF PHYSICS   Vol. 11   2009.2

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    DOI: 10.1088/1367-2630/11/2/025017

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  121. Intrinsic Spin Hall Effect in the s-Wave Superconducting State: Analysis of the Rashba Model

    Kontani H., Goryo J., Hirashima D. S.

    PHYSICAL REVIEW LETTERS   Vol. 102 ( 8 )   2009.2

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    DOI: 10.1103/PhysRevLett.102.086602

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  122. Intrinsic Spin Hall Effect in the s-Wave Superconducting State: Analysis of the Rashba Model Reviewed

    H. Kontani, J. Goryo, and D. S. Hirashima

    Physical Review Letters   Vol. 102   page: 086602   2009.2

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    A general expression for spin Hall conductivity (SHC) in the s-wave superconducting state at finite temperatures is derived. Based on the expression, we study SHC in a two-dimensional electron gas model in the presence of Rashba spin-orbit interaction (SOI). SHC is zero in the normal state, whereas it takes a large negative value as soon as the superconductivity occurs, due to the change in the quasiparticle contributions. Since this remarkable behavior is independent of the strength of the SOI, it will be widely observed in thin films of superconductors with surface-induced Rashba SOI, or in various noncentrosymmetric superconductors.

  123. Giant extrinsic spin Hall effect due to rare-earth impurities

    Tanaka T., Kontani H.

    NEW JOURNAL OF PHYSICS   Vol. 11   2009.1

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    DOI: 10.1088/1367-2630/11/1/013023

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  124. Giant Orbital Hall Effect in Transition Metals: Origin of Large Spin and Anomalous Hall Effects

    Kontani H., Tanaka T., Hirashima D. S., Yamada K., Inoue J.

    PHYSICAL REVIEW LETTERS   Vol. 102 ( 1 )   2009.1

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    DOI: 10.1103/PhysRevLett.102.016601

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  125. *Giant Orbital Hall Effect in Transition Metals: Origin of Large Spin and Anomalous Hall Effects Invited Reviewed

      Vol. 102   page: 016601   2009.1

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  126. Minimal model for study on Superconductivity in LaFeAsO1-xFx based on ab-initio downfolding

    Arita Ryotaro, Onari Seiichiro, Usui Hidetomo, Kuroki Kazuhiko, Tanaka Yukio, Kontani Hiroshi, Aoki Hideo

    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5   Vol. 150   2009

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    DOI: 10.1088/1742-6596/150/5/052010

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  127. Non-Fermi liquid behavior in the magnetotransport of quasi two-dimensional heavy Fermion compounds CeMIn5

    Nakajima Y., Shibauchi T., Shishido H., Nakai H., Behnia K., Izawa K., Hedo M., Uwatoko Y., Matsumoto T., Settai R., Onuki Y., Kontani H., Matsuda Y.

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   Vol. 69 ( 12 ) page: 3261 - 3264   2008.12

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    DOI: 10.1016/j.jpcs.2008.06.064

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  128. Spin Hall effect in Sr2RuO4 and transition metals (Nb,Ta)

    Tanaka T., Kontani H., Naito M., Hirashima D. S., Yamada K., Inoue J.

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   Vol. 69 ( 12 ) page: 3250-3252   2008.12

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    DOI: 10.1016/j.jpcs.2008.06.096

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  129. Impurity Effects in Sign-Reversing Fully Gapped Superconductors: Analysis of FeAs Superconductors

    Senga Yuko, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 77 ( 11 )   2008.11

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    DOI: 10.1143/JPSJ.77.113710

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  130. Unconventional superconductivity originating from disconnected Fermi surfaces in the iron-based oxypnictide

    Kuroki Kazuhiko, Onari Seiichiro, Arita Ryotaro, Usui Hidetomo, Tanaka Yukio, Kontani Hiroshi, Aoki Hideo

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 77   page: 96-98   2008.11

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  131. Intrinsic spin Hall effect in graphene: Numerical calculations in a multiorbital model

    Onari Seiichiro, Ishikawa Yasuhito, Kontani Hiroshi, Inoue Jun-ichiro

    PHYSICAL REVIEW B   Vol. 78 ( 12 )   2008.9

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    DOI: 10.1103/PhysRevB.78.121403

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  132. Unconventional pairing originating from the disconnected Fermi surfaces of superconducting LaFeAsO1-xFx

    Kuroki Kazuhiko, Onari Seiichiro, Arita Ryotaro, Usui Hidetomo, Tanaka Yukio, Kontani Hiroshi, Aoki Hideo

    PHYSICAL REVIEW LETTERS   Vol. 101 ( 8 )   2008.8

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    DOI: 10.1103/PhysRevLett.101.087004

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  133. Magnetotransport properties governed by antiferromagnetic fluctuations in the heavy-fermion superconductor CeIrIn5

    Nakajima Y., Shishido H., Nakai H., Shibauchi T., Hedo M., Uwatoko Y., Matsumoto T., Settai R., Onuki Y., Kontani H., Matsuda Y.

    PHYSICAL REVIEW B   Vol. 77 ( 21 )   2008.6

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    DOI: 10.1103/PhysRevB.77.214504

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  134. s-wave superconductivity due to Suhl-Kondo mechanism in Na(x)CoO(2)center dot yH(2)O: Effect of Coulomb interaction and trigonal distortion

    Yada Keiji, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 77 ( 18 )   2008.5

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    DOI: 10.1103/PhysRevB.77.184521

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  135. Theory of ac anomalous Hall conductivity in d-electron systems

    Tanaka T., Kontani H.

    PHYSICAL REVIEW B   Vol. 77 ( 19 )   2008.5

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    DOI: 10.1103/PhysRevB.77.195129

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  136. Intrinsic spin Hall effect and orbital Hall effect in 4d and 5d transition metals

    Tanaka T., Kontani H., Naito M., Naito T., Hirashima D. S., Yamada K., Inoue J.

    PHYSICAL REVIEW B   Vol. 77 ( 16 )   2008.4

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    DOI: 10.1103/PhysRevB.77.165117

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  137. Giant intrinsic spin and orbital hall effects in Sr2MO4 (M=Ru, Rh, Mo)

    Kontani H., Tanaka T., Hirashima D. S., Yamada K., Inoue J.

    PHYSICAL REVIEW LETTERS   Vol. 100 ( 9 )   2008.3

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    DOI: 10.1103/PhysRevLett.100.096601

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  138. Spin-Dependent Mass Enhancement under Magnetic Field in the Periodic Anderson Model Reviewed

    S. Onari, H. Kontani and Y. Tanaka,

    Journal of the Physical Society of Japan   Vol. 77   page: 023703   2008.2

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  139. Anomalous transport phenomena in Fermi liquids with strong magnetic fluctuations

    Kontani Hiroshi

    REPORTS ON PROGRESS IN PHYSICS   Vol. 71 ( 2 )   2008.2

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    DOI: 10.1088/0034-4885/71/2/026501

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  140. Spin-dependent mass enhancement under a magnetic field in the periodic Anderson model

    Onari Seiichiro, Kontani Hiroshi, Tanaka Yukio

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 77 ( 2 )   2008.2

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    DOI: 10.1143/JPSJ.77.023703

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  141. Intrinsic spin and orbital Hall effects in d- and f-electron systems

    Kontani H., Tanaka T., Naito M., Hirashima D. S., Yamada K., Inoue J.

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 77   page: 275-277   2008.1

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    DOI: 10.1143/JPSJS.77SA.275

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  142. Giant Intrinsic Spin and Orbital Hall Effects in Sr2MO4 (M=Ru,Rh,Mo) Reviewed

    H. Kontani, T. Tanaka, D.S. Hirashima, K. Yamada, J. Inoue

    Physical Review Letters   Vol. 100   page: 096601   2008

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  143. *Intrinsic spin Hall effect and orbital Hall effect in 4d and 5d transition metals Reviewed

    T. Tanaka, H. Kontani, M. Naito, T. Naito, D. S. Hirashima, K. Yamada, and J. Inoue

    Physical Review B   Vol. 77   page: 165117   2008

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    We study the intrinsic spin Hall conductivity (SHC) in various 5d transition metals (Ta, W, Re, Os, Ir, Pt, and Au) and 4d transition metals (Nb, Mo, Tc, Ru, Rh, Pd, and Ag) based on the Naval Research Laboratory tight-binding model, which enables us to perform quantitatively reliable analysis. In each metal, the obtained intrinsic SHC is independent of resistivity in the low resistive regime (ρ<50 μΩ cm) whereas it decreases in proportion to ρ−2 in the high resistive regime. In the low resistive regime, the SHC takes a large positive value in Pt and Pd, both of which have approximately nine d electrons per ion (nd=9). On the other hand, the SHC takes a large negative value in Ta, Nb, W, and Mo, where nd<5. In transition metals, a conduction electron acquires the trajectory-dependent phase factor that originates from the atomic wave function. This phase factor, which is reminiscent of the Aharonov–Bohm phase, is the origin of the SHC in paramagnetic metals and that of the anomalous Hall conductivity in ferromagnetic metals. Furthermore, each transition metal shows huge and positive d-orbital Hall conductivity (OHC), independent of the strength of the spin-orbit interaction. Since the OHC is much larger than the SHC, it will be possible to realize an orbitronics device made of transition metals.

  144. Intrinsic spin Hall effect in graphene: Numerical calculations in a multiorbital model Reviewed

    S. Onari, Y. Ishikawa, H. Kontani, and J. Inoue

    Physical Review B   Vol. 78   page: 121403R   2008

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  145. Unconventional pairing originating from the disconnected Fermi surfaces of superconducting LaFeAsO1-xFx Reviewed

    K. Kuroki, S. Onari, R. Arita, H. Usui, Y. Tanaka, H. Kontani and H. Aoki

    Physical Review Letters   Vol. 101   page: 087004   2008

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  146. Magnetotransport properties governed by antiferromagnetic fluctuations in the heavy-fermion superconductor CeIrIn5 Reviewed

    Y. Nakajima, H. Shishido, H. Nakai, T. Shibauchi, M. Hedo, Y. Uwatoko, T. Matsumoto, R. Settai, Y. Onuki, H. Kontani, and Y. Matsuda

    Physical Review B   Vol. 77   page: 0214504   2008

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  147. Theory of ac anomalous Hall conductivity in d -electron systems Reviewed

    T. Tanaka and H. Kontani

    Physical Review B   Vol. 77   page: 195129   2008

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  148. s-wave superconductivity due to Suhl-Kondo mechanism in NaxCoO2⋅yH2O: Effect of Coulomb interaction and trigonal distortion Reviewed

    K. Yada and H. Kontani

    Physical Review B   Vol. 77   page: 184521   2008

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  149. *Anomalous Transport Phenomena in Fermi Liquids with Strong Magnetic Fluctuations Invited Reviewed

    Hiroshi Kontani

    Reports on Progress in Physics   Vol. 71   page: 026501   2008

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    In many strongly correlated electron systems, remarkable violation of the relaxation time approximation (RTA) is observed. The most famous example would be high-Tc superconductors (HTSCs), and similar anomalous transport phenomena have been observed in metals near their antiferromagnetic (AF) quantum critical point (QCP). Here, we develop a transport theory involving resistivity and Hall coefficient on the basis of the microscopic Fermi liquid theory, by considering the current vertex correction (CVC). In nearly AF Fermi liquids, the CVC accounts for the significant enhancements in the Hall coefficient, magnetoresistance, thermoelectric power, and Nernst coefficient in nearly AF metals. According to the numerical study, aspects of anomalous transport phenomena in HTSC are explained in a unified way by considering the CVC, without introducing any fitting parameters; this strongly supports the idea that HTSCs are Fermi liquids with strong AF fluctuations. In addition, the striking \omega-dependence of the AC Hall coefficient and the remarkable effects of impurities on the transport coefficients in HTSCs appear to fit naturally into the present theory. The present theory also explains very similar anomalous transport phenomena occurring in CeCoIn5 and CeRhIn5, which is a heavy-fermion system near the AF QCP, and in the organic superconductor \kappa-(BEDT-TTF).

  150. Study of intrinsic spin and orbital Hall effects in Pt based on a (6s, 6p, 5d) tight-binding model Reviewed

    H. Kontani, M. Naito, D.S. Hirashima, K. Yamada and J. Inoue

    Journal of the Physical Society of Japan   Vol. 76   page: 103702   2007.10

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  151. Study of intrinsic spin and orbital hall effects in pt based on a (6s, 6p, 5d) tight-binding model

    Kontani Hiroshi, Naito Masayuki, Hirashima Dai S., Yamada Kosaku, Inoce Jun-Ichiro

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 76 ( 10 )   2007.10

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    DOI: 10.1143/JPSJ.76.103702

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  152. Striking similarities between HTSC and quasi-2D HFCeRIn5

    Izawa Koichi, Nakajima Y., Kasahara Y., Bel R., Behnia K., Shishido H., Settai R., Onuki Y., Kontani H., Matsuda Y.

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 460   page: 145 - 148   2007.9

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    DOI: 10.1016/j.physc.2007.04.004

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  153. Unusual Hall effect in quasi two-dimensional strongly correlated metal CeCoIn5

    Nakajima Y., Shishido H., Izawa K., Matsuda Y., Kontani H., Hedo H., Uwatoko Y., Matsumoto T., Settai R., Onuki Y.

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 460   page: 680 - 681   2007.9

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    DOI: 10.1016/j.physc.2007.03.082

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  154. Robustness of s-wave superconductivity against Coulomb interactions in NaxCoO2

    Yada Keiji, Kontani Hiroshi

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 460   page: 483-484   2007.9

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    DOI: 10.1016/j.physc.2007.03.045

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  155. Theory of thermal conductivity in high-T-c superconductors below T-c: Comparison between hole- and electron-doped systems

    Hara Hideyuki, Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 76 ( 7 )   2007.7

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    DOI: 10.1143/JPSJ.76.073705

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  156. Theory of Thermal Conductivity in High-Tc Superconductors below Tc: Comparison between Hole- and Electron-Doped Systems Reviewed

    Hideyuki Hara, Hiroshi Kontan

    Journal of the Physical Society of Japan   Vol. 76 ( 18 ) page: 184416   2007.7

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    In hole-doped high-Tc superconductors, thermal conductivity κ increases drastically just below Tc, which has been considered as a hallmark of a nodal gap. In contrast, such a coherence peak in κ is not visible in electron-doped compounds, which may indicate a full-gap state such as a d+is-wave state. To settle this problem, we study κ in the Hubbard model using the fluctuation-exchange (FLEX) approximation, which predicts that the nodal d-wave state is realized in both hole- and electron-doped compounds. The contrasting behavior of κ in both compounds originates from the differences in the hot/cold spot structure. In general, a prominent coherence peak in κ appears in line-node superconductors only when the cold spot exists on the nodal line.

  157. Theory of Infrared Hall Conductivity Based on the Fermi Liquid Theory: Analysis of High-Tc Superconductors Reviewed

      Vol. 76   page: 074707   2007.7

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  158. Theory of Thermal Conductivity in High-Tc Superconductors below Tc: Comparison between Hole- and Electron-Doped Systems Reviewed

    Hideyuki Hara, and Hiroshi Kontani

    Journal of the Physical Society of Japan   Vol. 76   page: 073705   2007.7

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  159. Theory of Infrared Hall Conductivity Based on the Fermi Liquid Theory: Analysis of High-Tc Superconductors Reviewed

    H. Kontani

    Journal of the Physical Society of Japan   Vol. 76 ( 07 ) page: 074707   2007.7

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    We study optical Hall conductivity for high-Tc superconductors on the basis of microscopic Fermi liquid theory. Current vertex corrections (CVCs) are correctly taken into account to satisfy the conservation laws, and are performed for the first time for optical conductivities based on the fluctuation-exchange (FLEX) approximation. We find that (I) the CVC emphasizes the ω-dependence of σxy(ω) significantly when the antiferromagnetic (AF) fluctuations are strong. For this reason, the relation σxy(ω)∼{σxx(ω)}2, which is satisfied in the extended Drude model given by the relaxation time approximation (RTA), is completely violated for a wide range of frequencies. Consequently, (II) the optical Hall coefficient RH(ω) strongly depends on ω below infrared frequencies, which is consistent with experimental observations. Interestingly, although σxx(ω) does not follow a simple Drude form due to the ω-dependence of the relaxation time τ, θH(ω) and σxy(ω) follow approximate simple Drude forms since the ω-dependences of τ and CVC almost cancel each other out. In conclusion, anomalous optical transport phenomena in high-Tc superconductors, which had been frequently assumed to be as evidence of the breakdown of the Fermi liquid state, can be well explained in terms of the nearly AF Fermi liquid once the CVC is taken into account.

  160. Theory of infrared hall conductivity based on the fermi liquid theory: Analysis of high-T-c superconductors

    Kontani Hiroshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 76 ( 7 )   2007.7

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    DOI: 10.1143/JPSJ.76.074707

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  161. Intrinsic anomalous Hall effect in ferromagnetic metals studied by the multi-d-orbital tight-binding model

    Kontani Hiroshi, Tanaka Takuro, Yamada Kosaku

    PHYSICAL REVIEW B   Vol. 75 ( 18 )   2007.5

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    DOI: 10.1103/PhysRevB.75.184416

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  162. Infrared Hall conductivity in optimally doped Bi2Sr2CaCu2O8+δ : Drude behavior examined by experiment and fluctuation-exchange-model calculations Reviewed

    D.C. Schmadel, G. S. Jenkins, J.J. Tu, G.D. Gu, H. Kontani, and H. D. Drew

    Physical Review B   Vol. 75 ( 14 ) page: 140506R (4p)   2007.4

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    The temperature dependence of the Hall conductivity is reported at mid- and far-IR frequencies for cleaved single crystals. A nearly simple Drude behavior is observed with a scattering rate that is linear in temperature and nearly frequency independent. The Hall data are in good agreement with calculations based on the fluctuation-exchange interaction when current vertex corrections are included. The σxy quasiparticle spectral weight is suppressed to 0.09 times the band value, compared with 0.33 times the band value for σxx.

  163. Infrared Hall conductivity in optimally doped Bi2Sr2CaCu2O8+delta: Drude behavior examined by experiment and fluctuation-exchange-model calculations

    Schmadel D. C., Jenkins G. S., Tu J. J., Gu G. D., Kontani Hiroshi, Drew H. D.

    PHYSICAL REVIEW B   Vol. 75 ( 14 )   2007.4

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    DOI: 10.1103/PhysRevB.75.140506

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  164. Hall effect in the quasi two-dimensional strongly correlated metal CeMIn5 (M = Co, Rh)

    Nakajima Y., Shishido H., Nakai H., Shibauchi T., Izawa K., Behnia K., Hedo H., Uwatoko Y., Matsumoto T., Settai R., Onuki Y., Kontani H., Matsuda Y.

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: 334 - 336   2007.3

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    DOI: 10.1016/j.jmmm.2006.10.028

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  165. Anomalous transport phenomena in CeCoIn5 close to quantum critical point

    Onari S., Kontani H., Tanaka Y.

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: 359-361   2007.3

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    DOI: 10.1016/j.jmmm.2006.10.070

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  166. Renormalization of Coulomb interactions in s-wave superconductor NaxCoO2

    Yada Keiji, Kontani Hiroshi

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: 684 - 686   2007.3

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    DOI: 10.1016/j.jmmm.2006.10.192

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  167. Nonlocal effect of local nonmagnetic impurity in high-T-c superconductors: Induced local moment and huge residual resistivity

    Kontani Hiroshi, Ohno Masanori

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: 483-485   2007.3

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    DOI: 10.1016/j.jmmm.2006.10.862

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  168. Non-fermi liquid behavior in the magnetotransport of CeMln(5) (M : Co and Rh): Striking similarity between quasi two-dimensional heavy fermion and high-T-c cuprates

    Nakajima Y., Shishido H., Nakai H., Shibauchi T., Behnia K., Izawa K., Hedo M., Uwatoko Y., Matsumoto T., Settai R., Onuki Y., Kontani H., Matsuda Y.

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 76 ( 2 )   2007.2

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    DOI: 10.1143/JPSJ.76.024703

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  169. Non-Fermi Liquid Behavior in the Magnetotransport of CeMIn5 (M: Co and Rh): Striking Similarity between Quasi Two-Dimensional Heavy Fermion and High-Tc Cuprates Reviewed

    Y. Nakajima, H. Shishido, H. Nakai, T. Shibauchi, K. Behnia, K. Izawa, M. Hedo, Y. Uwatoko, T. Matsumoto, R. Settai, Y. Ōnuki, H. Kontani, and Y. Matsuda

    Journal of the Physical Society of Japan   Vol. 76 ( 02 ) page: 024703   2007.2

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    We present a systematic study of the dc-resistivity, Hall effect, and magnetoresistance in the normal state of quasi two-dimensional (2D) heavy fermion superconductors CeMIn5 (M: Rh and Co) under pressure. Here the electronic system evolves with pressure from an antiferromagnetic (AF) metal, through a highly unconventional non-Fermi liquid, and finally into a Fermi-liquid state. The novelty of these materials is best highlighted when compared with LaMIn5, a system with similar electronic structures, which shows a nearly temperature independent Hall coefficient and a magnetoresisitance which is well described by the classical Kohler's rule. In sharp contrast, in CeMIn5, the amplitude of the Hall coefficient increases dramatically with decreasing temperature, reaching at low temperatures a value significantly larger than 1/ne, where n is the carrier number. Furthermore, the magnetoresistance is characterized by T- and H-dependence which clearly violate Kohler's rule. We found that the cotangent of the Hall angle cot ΘH varies as T2, and the magnetoresistance is well scaled by the Hall angle as Δρxx/ρxx∝tan 2ΘH. These non-Fermi liquid properties in the electron transport are remarkably pronounced when the AF fluctuations are enhanced in the vicinity of the quantum critical point. We lay particular emphasis on the striking resemblance of these anomalous magnetotransport with those of the high-Tc cuprates. We argue that features commonly observed in quasi 2D heavy fermion and cuprates very likely capture universal features of strongly correlated electron systems in the presence of strong AF fluctuations, holding the promise of bridging our understanding of heavy fermion systems and high-Tc cuprates.

  170. Degeneracy dependence of the Kadowaki-Woods relation in heavy-fermion systems

    Tsujii Naohito, Kontani Hiroshi, Yoshimura Kazuyoshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 76   page: 174-177   2007.1

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    DOI: 10.1143/JPSJS.76SA.174

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  171. Intrinsic anomalous Hall effect in ferromagnetic metals studied by the multi- d -orbital tight-binding model Reviewed

    Hiroshi Kontani, Takuro Tanaka, and Kosaku Yamada

    Physical Review B   Vol. 75 ( 18 ) page: 184416   2007

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    To elucidate the origin of anomalous Hall effect (AHE) in ferromagnetic transition metals, we study the intrinsic AHE based on a multiorbital (dxz,dyz) tight-binding model. We find that a large anomalous velocity comes from the off-diagonal (interorbital) hopping. For this reason, the present model shows a large intrinsic anomalous Hall conductivity (AHC) which is compatible with typical experimental values in ferromagnets (102–103 Ω−1 cm−1), without the necessity to assume a special band structure at the Fermi level. In good metals where ρ is small, the intrinsic AHC is constant (dissipationless) as found by Karplus and Luttinger. In bad metals, however, we find that the AHC is proportional to ρ−2 when &#8463;∕2τ is larger than the minimum band splitting measured from the Fermi level Δ. This crossover behavior of the intrinsic AHE, which was derived in J. Phys. Soc. Jpn. 63, 2627 (1994), was recently observed in various ferromagnetic metals universally by Asamitsu We also stress that the present (dxz,dyz) tight-binding model shows a huge spin Hall effect in a paramagnetic state.

  172. Optical conductivity of bad metals: Shift of the Drude peak

    T. Mutou and H. Kontani

    Physical Review B   Vol. 74 ( 11 ) page: 115107 (6p)   2006.12

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  173. Theoretical study of the phase diagram of beta '-(BEDT-TTF)(2)AuCl2 at hydrostatic pressure

    Kino Hiori, Kontani Hiroshi, Miyazaki Tsuyoshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 10 )   2006.10

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    DOI: 10.1143/JPSJ.75.104702

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  174. Optical conductivity of bad metals: Shift of the Drude peak

    Mutou Tetsuya, Kontani Hiroshi

    PHYSICAL REVIEW B   Vol. 74 ( 11 )   2006.9

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    DOI: 10.1103/PhysRevB.74.115107

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  175. Effect of a nonmagnetic impurity in a nearly antiferromagnetic Fermi liquid: Magnetic correlations and transport phenomena

    Kontani Hiroshi, Ohno Masanori

    PHYSICAL REVIEW B   Vol. 74 ( 1 )   2006.7

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    DOI: 10.1103/PhysRevB.74.014406

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  176. Transport phenomena in a three-dimensional system close to the magnetic quantum critical point: The conserving approximation with current vertex corrections, Reviewed

    S. Onari, H. Kontani, and Y. Tanaka,

    Physical Review B   Vol. 74 ( 22 ) page: 224434 (10p)   2006.6

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    It is known that various transport coefficients strongly deviate from conventional Fermi-liquid behaviors in many electron systems which are close to antiferromagnetic (AF) quantum critical points (QCP). For example, Hall coefficients and Nernst coefficients in three-dimensional heavy fermion CeCoIn5 and CeCu6–xAux increase strikingly at low temperatures, whose overall behaviors are similar to those in high-Tc cuprates. These temperature dependencies are too strong to explain in terms of the relaxation time approximation. To elucidate the origin of these anomalous transport phenomena in three-dimensional systems, we study the current vertex corrections (CVC) based on the fluctuation exchange approximation, and find out the decisive role of the CVC. The main finding of the present paper is that the Hall coefficient and the Nernst coefficient strongly increase thanks to the CVC in the vicinity of the AF QCP, irrespective of dimensionality. We also study the relaxation time of quasiparticles, and find that "hot points" and "cold lines" are formed in general three-dimensional systems due to strong AF fluctuations.

  177. Effect of a nonmagnetic impurity in a nearly antiferromagnetic Fermi liquid: Magnetic correlations and transport phenomena Reviewed

    H. Kontani and M. Ohno

    Physical Review B   Vol. 74 ( 01 ) page: 014406 (21p)   2006.6

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    In nearly antiferromagnetic (AF) metals such as high-Tc superconductors (HTSCs), a single nonmagnetic impurity frequently causes nontrivial widespread change of the electronic states. To elucidate this long-standing issue, we study a Hubbard model with a strong onsite impurity potential based on an improved fluctuation-exchange (FLEX) approximation, which we call the GVI-FLEX method. This model corresponds to the HTSC with dilute nonmagnetic impurity concentration. We find that (i) both local and staggered susceptibilities are strongly enhanced around the impurity. By this reason, (ii) the quasiparticle lifetime as well as the local density of states are strongly suppressed in a wide area around the impurity (like a Swiss cheese hole), which causes the "huge residual resistivity" beyond the s-wave unitary scattering limit. We stress that the excess quasiparticle damping rate caused by impurities has strong k-dependence due to non-s-wave scatterings induced by many-body effects, so the structure of the "hot spot/cold spot" in the host system persists against impurity doping. This result could be examined by the ARPES measurements. In addition, (iii) only a few percent of impurities can cause a "Kondo-like" upturn of resistivity (d/dT<0) at low T when the system is very close to the AF quantum critical point. The results (i)–(iii) obtained in the present study, which cannot be derived by the simple FLEX approximation, naturally explain the main impurity effects in HTSCs. We also discuss the impurity effect in heavy fermion systems and organic superconductors.

  178. Transport phenomena in a three-dimensional system close to the magnetic quantum critical point: The conserving approximation with current vertex corrections

    Onari Seiichiro, Kontani Hiroshi, Tanaka Yukio

    PHYSICAL REVIEW B   Vol. 73 ( 22 )   2006.6

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    DOI: 10.1103/PhysRevB.73.224434

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  179. Grand Kadowaki-Woods relation of heavy-fermion systems with degeneracy

    Tsujii N., Kontani H., Yoshimura K.

    PHYSICA B-CONDENSED MATTER   Vol. 378-80   page: 730 - 731   2006.5

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    DOI: 10.1016/j.physb.2006.01.462

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  180. Electron-Phonon Mechanism for Superconductivity in Na0.35CoO2: Valence-Band Suhl-Kondo Effect Driven by Shear Phonons Reviewed

    K. Yada and H. Kontai

    Journal of the Physical Society of Japan   Vol. 75 ( 3 ) page: 033705 (4p)   2006.3

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    To study the possible mechanism of superconductivity in Na0.35CoO2, we examine the interaction between all the relevant optical phonons (breathing and shear phonons) and t2g (a1g+eg') electrons of Co ions, and study the transition temperature for s-wave superconductivity. The obtained Tc is very low when the eg' valence bands are far below the Fermi level. However, Tc is strongly enhanced when the top of the eg' valence bands is close to the Fermi level (e.g., -50 meV), thanks to the interband hopping of Cooper pairs caused by shear phonons. This “valence-band Suhl–Kondo mechanism" due to shear phonons is important in understanding the superconductivity in Na0.35CoO2. By the same mechanism, the kink structure of the band dispersion observed by angle-resolved photoemission spectroscopy (ARPES) measurements, which indicates the strong mass enhancement (m*/m∼3) due to optical phonons, is also explained.

  181. Theoretical Study of the Phase Diagram of β'-(BEDT-TTF)2AuCl2 at Hydrostatic Pressure Reviewed

    Journal of the Physical Society of Japan   Vol. 75 ( 10 ) page: 104702 (4)   2006.3

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    We study the electronic structure of β'-(BEDT-TTF)2AuCl2 under hydrostatic pressures of up to 20 GPa. We employ the effective single-band Hubbard model, the band structure of which is based on the first-principles result, and apply the FLEX approximation to take into account of the effective on-site Coulomb interaction. We examine magnetic and superconducting instabilities to find that the resulting theoretical phase diagram shows that the N&eacute;el temperature is high under hydrostatic pressure. In contrast to β'-(BEDT-TTF)2ICl2, β'-(BEDT-TTF)2AuCl2 is expected to show no superconducting state.

  182. Electron-phonon mechanism for superconductivity in Na0.35CoO2: Valence-band Suhl-Kondo effect driven by shear phonons

    Yada K, Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 3 )   2006.3

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    DOI: 10.1143/JPSJ.75.033705

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  183. Evolution of Hall coefficient in two-dimensional heavy fermion CeCoIn5

    Nakajima Y, Izawa K, Matsuda Y, Behnia K, Kontani H, Hedo M, Uwatoko Y, Matsumoto T, Shishido H, Settai R, Onuki Y

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 2 )   2006.2

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    DOI: 10.1143/JPSJ.75.023705

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  184. Evolution of Hall Coefficient in Two-Dimensional Heavy Fermion CeCoIn5 Reviewed

    Y. Nakajima, K. Izawa, Y. Matsuda, K. Behnia, H. Kontani, M. Hedo, Y. Uwatoko, T. Matsumoto, H. Shishido, R. Settai and Y. Onuki

    Journal of the Physical Society of Japan   Vol. 2006 ( 1 ) page: 023705(4p)   2006.1

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    We report on the pressure dependence of the Hall coefficient RH in quasi-2D heavy fermion CeCoIn5. At ambient pressure, below a temperature associated with the emergence of non-Fermi liquid properties, RH is anomalously enhanced. We found that the restoration of the Fermi liquid state with applied pressure leads to a gradual suppression of this dramatic enhancement. Moreover, the enhancement in RH was found to be confined to an intermediate temperature window, where inelastic electron-electron scattering is dominant. Our results strongly support the presence of cold and hot spots on the Fermi surface probably due to anisotropic scattering by antiferromagnetic fluctuations, which may also prove relevant for the debate on the anomalous normal-state properties of high-Tc cuprates.

  185. Optical Conductivity and Hall Coefficient in High-Tc Superconductors: Significant Role of Current Vertex Corrections Reviewed

    Hiroshi Kontani

    Journal of the Physical Society of Japan   Vol. 75 ( 1 ) page: 013703(4p)   2006.1

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    We study AC conductivities in high-Tc cuprates, which offer us significant information to determine the true ground states. We take the current vertex correction (CVC) into account correctly to satisfy the conservation laws in terms of the fluctuation-exchange (FLEX) approximation. The significant role of the CVC on the optical Hall conductivity [σxy(ω)] is confirmed in the presence of strong antiferromagnetic (AF) fluctuations. This fact leads to the failure of the relaxation time approximation (RTA). As a result, experimental highly unusual behaviors, (i) prominent ω and temperature dependences of the optical Hall conductivity and the optical Hall coefficient [RH(ω)], and (ii) a simple Drude form of the optical Hall angle [θH(ω)] for a wide range of ω, are satisfactorily reproduced. In conclusion, both DC and AC transport phenomena in (slightly under-doped) high-Tc cuprates can be explained comprehensively in terms of a nearly AF Fermi liquid, without assuming an exotic ground state.

  186. Optical conductivity and hall coefficient in high-T-c superconductors: Significant role of current vertex corrections

    Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 1 )   2006.1

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    DOI: 10.1143/JPSJ.75.013703

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  187. Physical meaning of the current vertex corrections: DC and AC transport phenomena in high-T-c superconductors

    Kontani Hiroshi

    Low Temperature Physics, Pts A and B   Vol. 850   page: 565-566   2006

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  188. Spin fluctuations and weak pseudogap behaviors in Na0.35CoO2: Renormalization of band structure

    Yada Keiji, Kontani Hiroshi

    LOW TEMPERATURE PHYSICS, PTS A AND B   Vol. 850   page: 707-+   2006

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  189. 軌道縮退を有する重い電子系のGrand Kadowaki-Woods則 Invited Reviewed

    辻井直人、紺谷浩、吉村一良

    日本物理学会誌   Vol. 60 ( 11 ) page: 872-875   2005.11

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  190. Origin of Weak Pseudogap Behaviors in Na0.35CoO2: Absence of Small Hole Pockets Reviewed

    Keiji Yada and Hiroshi Kontani

    Journal of the Physical Society of Japan   Vol. 74 ( 8 ) page: 2161-2164   2005.8

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    We analyze the normal electronic states of Na0.35CoO2 based on the effective d- p model with a full d-orbital freedom using the fluctuation-exchange (FLEX) approximation. The electronic states sensitively depend on the topology of Fermi surfaces, which changes with the crystalline electric splitting (CES) due to the trigonal deformation. We succeed in reproducing the weak pseudogap behaviors in the density of states (DOS) and in the uniform magnetic susceptibility below 300 K, assuming that six small hole pockets predicted by LDA band calculations are absent. If these pockets exist, on the contrary, “anti-pseudogap behaviors" should inevitably appear. Thus, the present study strongly supports the absence of the small hole pockets in Na0.35CoO2, as reported by recent ARPES measurements. A large Fermi surface around the Γ-point would account for the superconductivity in water-intercalated samples.

  191. Origin of weak pseudogap behaviors in Na0.35CoO2: Absence of small hole pockets

    Yada K, Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 74 ( 8 ) page: 2161 - 2164   2005.8

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    DOI: 10.1143/JPSJ.74.2161

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  192. Generalized Kadowaki-Woods relation in Er- and Sm-based heavy fermion systems

    Kontani H

    PHYSICA B-CONDENSED MATTER   Vol. 359   page: 202-204   2005.4

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    DOI: 10.1016/j.physb.2005.01.036

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  193. Universality in heavy fermion systems with general degeneracy

    Tsujii N, Kontani H, Yoshimura K

    PHYSICAL REVIEW LETTERS   Vol. 94 ( 5 )   2005.2

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    DOI: 10.1103/PhysRevLett.94.057201

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  194. *Universality in Heavy Fermion Systems with General Degeneracy Reviewed

    N. Tsujii, H. Kontani, and K. Yoshimura

    Physical Review Letter   Vol. 94 ( 11 ) page: 057201(4p)   2005.2

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    We discuss the relation between the T2 coefficient of electrical resistivity A and the T-linear specific-heat coefficient γ for heavy-fermion systems with general N, where N is the degeneracy of quasiparticles. A set of experimental data reveals that the Kadowaki-Woods relation, A/γ2=1×10-5&#8201;&#8201;μΩ&#8201;cm(K&#8201;mol/mJ)2, collapses remarkably for large-N systems, although this relation has been regarded to be commonly applicable to the Fermi liquids. Instead, based on the Fermi-liquid theory we propose a new relation, A˜/γ˜2=1×10-5 with A˜=A/1/2N(N-1) and γ˜=γ/1/2N(N-1). This new relation exhibits an excellent agreement with the data for the whole range of degenerate heavy fermions.

  195. From Kondo Effect to Fermi Liquid Invited Reviewed

    Hiroshi Kontani and Kosaku Yamada

    Journal of the Physical Society of Japan   Vol. 74 ( 1 ) page: 155-166   2005.1

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    The Kondo effect has been playing an important role in strongly correlated electon systems. The important point is that the magnetic impurity in metals is a typical example of the Fermi liquid. In the system the local spin is conserved in the ground state and continuity with respect to Coulomb repulsion U is satisfied. This nature is satisfied also in the periodic systems as far as the systems remain as the Fermi liquid. This property of the Fermi liquid is essential to understand the cuprate high-Tc superconductors (HTSC). On the basis of the Fermi liquid theory we develop the transport theory such as the resistivity and the Hall coefficient in strongly correlated electron systems, such as HTSC, organic metals and heavy Fermion systems. The significant role of the vertex corrections for total charge- and heat-currents on the transport phenomena is explained. By taking the effect of the current vertex corrections into account, various typical non-Fermi-liquid-like transport phenomena in systems with strong magnetic and/or superconducting flucutations are explained within the Fermi liquid theory.

  196. Magnetic-Field-induced Antiferromagnetism in Two-dimensional Hubbard Model: Analysis of CeRhIn5 Reviewed

    Keitaro Sakurazawa, Hiroshi Kontani and Tetsuro Saso

    Journal of the Physical Society of Japan   Vol. 74 ( 1 ) page: 271-274   2005.1

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    We propose a mechanism for the magnetic-field-induced antiferromagnetic (AF) state in a two-dimensional Hubbard model in the vicinity of the AF quantum critical point (QCP), using the fluctuation-exchange (FLEX) approximation by taking the Zeeman energy due to the magnetic field B into account. In the vicinity of the QCP, we find that the AF correlation perpendicular to B is enhanced, whereas that parallel to B is reduced. This fact means that the finite magnetic field increases TN, with the AF order perpendicular to B. The increment of TN can be understood in terms of the reduction of both quantum and thermal fluctuations due to the magnetic field, which is caused by the self-energy effect within the FLEX approximation. The present study naturally explains the increment of TN in CeRhIn5 under the magnetic field found recently. We will also discuss a relation to some organic metals.

  197. From Kondo effect to Fermi liquid

    Kontani H, Yamada K

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 74 ( 1 ) page: 155 - 166   2005.1

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    DOI: 10.1143/JPSJ.74.155

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  198. Magnetic-field-induced antiferromagnetism in two-dimensional Hubbard model: Analysis of CeRhIn5

    Sakurazawa K, Kontani H, Saso T

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 74 ( 1 ) page: 271 - 274   2005.1

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    DOI: 10.1143/JPSJ.74.271

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  199. Generalized Kadowaki-Woods relation in Er- and Sm-based Heavy Fermion Systems, Invited Reviewed

    Hiroshi Kontani

    Physica B.   Vol. 359-361   page: 202-204   2005

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  200. Theory of anisotropic s-wave superconductivity with point-node-like gap minima: Analysis of (Y,Lu)Ni2B2C Reviewed

    H. Kontani

    Physical Review B   Vol. 70 ( 5 ) page: 054507(13p)   2004.8

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    Recent intensive experimental studies revealed that (Y,Lu)Ni2B2C is an extremely anisotropic s-wave superconductor. In addition, its gap function possesses deep point minima, whose ratio of the gap anisotropy is more than 10. On the theoretical side, however, it is nontrivial to understand the origin of such a peculiar superconductivity. In the present paper, we propose a mechanism of the s-wave superconductivity with deep gap minima, based on the theoretical model where strong electron-phonon coupling as well as the moderate magnetic fluctuations coexist. By analyzing the strong coupling Eliashberg equation, we find that s-wave superconducting gap function owing to the electron-phonon coupling becomes highly anisotropic as the magnetic fluctuations increase. The set of model parameters for realizing the strong gap anisotropy in the present model will be appropriate for (Y,Lu)Ni2B2C. According to the present mechanism, (groups of) pairs of gap minima appear at points on the Fermi surface which are connected by the nesting vector Q, in both cases of s-wave superconductors and non-s-wave ones. We briefly discuss other superconductors with highly anisotropic gap function, e.g., PrOs4Sb12 and Na0.33CoO2.

  201. Theory of anisotropic s-wave superconductivity with point-node-like gap minima: Analysis of (Y,Lu)Ni2B2C

    Kontani H

    PHYSICAL REVIEW B   Vol. 70 ( 5 )   2004.8

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    DOI: 10.1103/PhysRevB.70.054507

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  202. Generalized Kadowaki-Woods Relation in Heavy Fermion Systems with Orbital Degeneracy Reviewed

    Hiroshi Kontani

    Journal of Physical Society of Japan   Vol. 73 ( 3 )   2004.3

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    We present a theoretical study of the Kadowaki-Woods relation in the orbitally degenerate periodic Anderson model. Based on the Fermi liquid theory, we derive the generalized Kadowaki-Woods relationin the strong coupling limit, Aγ-2 \approx 10-5 /&frac12; N(N-1) [&micro;Ω cm (mol&middot;K/mJ)2], where A is the coefficient of the T2 term in the resistivity, γ is the T-linear specific heat coefficient, and N is the f-orbital degeneracy. This result naturally explains the remarkably smaller value of Aγ-2 in various orbitally degenerate (mainly Yb-based) heavy Fermion systems, reported by Tsujii et al. [J. Phys.: Condens. Matter 15 (2003) 1993].

  203. Generalized Kadowaki-Woods relation in heavy fermion systems with orbital degeneracy

    Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 73 ( 3 ) page: 515 - 518   2004.3

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    DOI: 10.1143/JPSJ.73.515

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  204. Normal-state Hall Angle and Magnetoresistance in Quasi-2D Heavy Fermion CeCoIn5 near a Quantum Critical Point Reviewed

    Y. Nakajima, K. Izawa, Y. Matsuda, S. Uji, T. Terashima, H. Shishido, R. Settai, Y. Onuki and H. Kontani

    Journal of Physical Society of Japan   Vol. 73 ( 1 ) page: 5-8   2004.1

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    The normal-state Hall effect and magnetoresisitance (MR) have been measured in the quasi two dimensional (2D) heavy fermion superconductor CeCoIn5. In the non-Fermi liquid region where the reistivity ρxx exhibits an almost perfect T-linear dependence, the Hall angle varies as cot θH ∝ T2 and MR displays a strong violation of Kohler's rule. We demonstrate a novel relation between the MR and the Hall conductivity, Δ ρxx/ρxx∝ (σxyρxx)2. These results bear a striking resemblance to the normal-state properties of high-Tc cuprates, indicating universal transport properties in the presence of quasi-2D antiferromagnetic fluctuations near a quantum critical point.

  205. Phase Diagram of β'-(BEDT-TTF)2ICl2 under High Pressure Based on the First-Principles Electronic Structure Reviewed

    Hiori Kino, Hiroshi Kontani and Tsuyoshi Miyazaki

    Journal of Physical Society of Japan   Vol. 73 ( 1 ) page: 25-28   2004.1

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    We present a theoretical study on the superconductivity of β'-(BEDT-TTF)2ICl2 at Tc=14.2 K under a high hydrostatic pressure recently found, which is the highest among organic superconductors. In the present work, we study an effective model using the fluctuation-exchange (FLEX) approximation based on the results of first-principles calculation. In the obtained phase diagram, the superconductivity with dxy-like symmetry is realized next to the antiferromagnetic phase, as a result of the one-dimensional to two-dimensional crossover driven by the pressure.

  206. Phase diagram of beta '-(BEDT-TTF)(2)ICl2 under high pressure based on the first-principles electronic structure

    Kino H, Kontani H, Miyazaki T

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 73 ( 1 ) page: 25 - 28   2004.1

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    DOI: 10.1143/JPSJ.73.25

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  207. Normal-state hall angle and magnetoresistance in Quasi-2D heavy fermion CeCoIn5 near a quantum critical point

    Nakajima Y, Izawa K, Matsuda Y, Uji S, Terashima T, Shishido H, Settai R, Onuki Y, Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 73 ( 1 ) page: 5 - 8   2004.1

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    DOI: 10.1143/JPSJ.73.5

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  208. 高温超伝導体の以上金属相における輸送現象の理論 ─フェルミ液体論に基づく統一的理論─ Invited Reviewed

    紺谷浩

    日本物理学会誌   Vol. 58 ( 7 ) page: 524-527   2003.7

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  209. Origin of superconductivity in beta(')-(BEDT-TTF)(2)ICl2 under high pressure and in beta-(BEDT-TTF)(2)X at atmospheric pressure

    Kontani H

    PHYSICAL REVIEW B   Vol. 67 ( 18 )   2003.5

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    DOI: 10.1103/PhysRevB.67.180503

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  210. Theory of Nernst coefficient in high-T-c cuprates: the role of vertex corrections

    Kontani H

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 388   page: 68 - 69   2003.5

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    DOI: 10.1016/S0921-4534(02)02638-2

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  211. Nernst coefficient in high-T-c superconductors: The role of superconducting fluctuations

    Kontani H

    ACTA PHYSICA POLONICA B   Vol. 34 ( 2 ) page: 799 - 802   2003.2

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  212. General formula for the thermoelectric transport phenomena based on Fermi liquid theory: Thermoelectric power, Nernst coefficient, and thermal conductivity

    Kontani H

    PHYSICAL REVIEW B   Vol. 67 ( 1 )   2003.1

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    DOI: 10.1103/PhysRevB.67.014408

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  213. Nernst coefficient and magnetoresistance in high-T-c superconductors: The role of superconducting fluctuations

    Kontani H

    PHYSICAL REVIEW LETTERS   Vol. 89 ( 23 )   2002.12

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    DOI: 10.1103/PhysRevLett.89.237003

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  214. Nernst Coefficient and Magnetoresistance in High-Tc Superconductors: The Role of Superconducting Fluctuations Reviewed

    Hiroshi Kontani

    Physical Review Letter   Vol. 89 ( 23 ) page: 237003(4p)   2002.11

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    In high-Tc cuprates, the Nernst coefficient (ν) as well as the magnetoresistance (Δρ/ρ) increases drastically below the pseudogap temperature, T*, which attracts much attention as a key phenomenon in the pseudogap region. We study these transport phenomena in terms of the fluctuation-exchange+T–matrix approximation. In this present theory, the d-wave superconducting (SC) fluctuations, which are mediated by antiferromagnetic (AF) correlations, become dominant below T*. We especially investigate the vertex corrections both for the charge current and the heat one to keep the conservation laws. As a result, the mysterious behaviors of ν and Δρ/ρ are naturally explained as the reflection of the enhancement of the SC fluctuation, without assuming thermally excited vortices. The present result suggests that the pseudogap phenomena are well described in terms of the Fermi liquid with AF and SC fluctuations.

  215. Theory of magnetoresistance in correlated electron systems: modified Kohler rule in high-T-c superconductors

    Kontani H

    PHYSICA B-CONDENSED MATTER   Vol. 312   page: 25 - 27   2002.3

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    DOI: 10.1016/S0921-4526(01)01158-9

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  216. Theory of Thermoelectric Power in High-Tc Superconductors Reviewed

    Hiroshi Kontani

    Journal of the Physical Society of Japan   Vol. 2001 ( 6 ) page: 2840-2843   2001.10

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    We present a microscopic theory for the thermoelectric power (TEP) in high-Tc cuprates. Based on the general expression for the TEP, we perform the calculation of the TEP for a two-dimensional Hubbard model including all the vertex corrections necessary to satisfy the conservation laws. In the present study, characteristic anomalous temperature and doping dependences of the TEP in high-Tc cuprates, which have been a long-standing problem in high-Tc cuprates, are well reproduced for both hole- and electron-doped systems, except for the heavily under-doped case. According to the present analysis, the strong momentum and energy dependences of the self-energy due to the strong antiferromagnetic fluctuations play an essential role in reproducing experimental anomalies of the TEP.

  217. Theory of thermoelectric power in high T-c superconductors

    Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 70 ( 10 ) page: 2840 - 2843   2001.10

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    DOI: 10.1143/JPSJ.70.2840

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  218. General formula for the magnetoresistance on the basis of Fermi liquid theory

    Kontani H

    PHYSICAL REVIEW B   Vol. 64 ( 5 )   2001.8

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    DOI: 10.1103/PhysRevB.64.054413

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  219. General formula for the magnetoresistance on the basis of Fermi liquid theory Reviewed

    Hiroshi Kontani

    Physical Review B.   Vol. 64 ( 5 ) page: 054413(19p)   2001.8

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  220. Magnetoresistance in High-Tc Superconductors: The Role of Vertex Corrections Reviewed

    Hiroshi Kontani

    Journal of the Physical Society of Japan   Vol. 70 ( 7 ) page: 1873-1876   2001.7

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    In high-Tc cuprates, the orbital magnetoresistance in plane (Δρ/ρ) is anomalously enhanced at lower tempemeratures compared with conventional Fermi liquids, and thus Kohler's rule is strongly violated. Moreover, it should be noted that an intimate relation between Δρ/ρ and the Hall coefficient (RH), Δρ/ρ ∝ (RH/ρ)2, holds well experimentally, and is called the “modified Kohler's rule". In this letter, we study this long-standing problem in terms of the nearly antiferromagnetic (AF) Fermi liquid. We analyze the exact expression for Δρ/ρ by including the vertex corrections (VC's) to keep the conservation laws, and find the approximate relation Δρ/ρ ∝ ξAF4 ρ-2 &middot; H2 (ξAF being the AF correlation length) in the presence of AF fluctuations. The factor ξAF4, which comes from the VC's for the current, gives the additional temperature dependence. By taking account of the relation RH ∝ ξAF2 [Kontani et al.: Phys. Rev. B 59 (1999) 14723], we can naturally explain the modified Kohler's rule. In conclusion, based on the Fermi liquid theory, the famous seemingly non-Fermi liquid behaviors of RH and Δρ/ρ in high-Tc cuprates are naturally understood on an equal footing.

  221. Possible appearance of superconductivity on Si(100) surface

    Kino H, Kontani H

    SURFACE SCIENCE   Vol. 482   page: 501 - 506   2001.6

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    DOI: 10.1016/S0039-6028(00)01029-3

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  222. Theory of the Hall coefficient and resistivity for the layered organic superconductors kappa-(BEDT-TTF)(2)X

    Kontani H, Kino H

    PHYSICAL REVIEW B   Vol. 63 ( 13 )   2001.4

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    DOI: 10.1103/PhysRevB.63.134524

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  223. Comment on "Charge-orbital stripe structure in La1-xCaxMnO3 (x=1/2, 2/3)" - Reply

    Mutou T, Kontani H

    PHYSICAL REVIEW LETTERS   Vol. 86 ( 11 ) page: 2479 - 2479   2001.3

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    DOI: 10.1103/PhysRevLett.86.2479

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  224. Comment on "Charge-orbital stripe structure in La1-xCaxMnO3 (x=1/2, 2/3)"

    Hotta T, Dagotto E, Koizumi H, Takada Y

    PHYSICAL REVIEW LETTERS   Vol. 86 ( 11 ) page: 2478 - 2478   2001.3

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    DOI: 10.1103/PhysRevLett.86.2478

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  225. Hall effect in high-T-c superconductors

    Kontani H, Kanki K, Ueda K

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   Vol. 62 ( 1-2 ) page: 83 - 87   2001

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    DOI: 10.1016/S0022-3697(00)00105-0

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  226. Possible appearance of superconductivity on Si(001) surface

    Kino H, Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 69 ( 7 ) page: 1962 - 1965   2000.7

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    DOI: 10.1143/JPSJ.69.1962

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  227. Origin of the charge-ordered stripe with the orbital ordering in manganese oxides

    Mutou T, Kontani H

    PHYSICA B   Vol. 281   page: 531 - 533   2000.6

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    DOI: 10.1016/S0921-4526(99)01041-8

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  228. Anomalous behaviors of the transport phenomena in high-T-c superconductors

    Kontani H, Kanki K, Ueda K

    PHYSICA B   Vol. 281   page: 808 - 809   2000.6

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    DOI: 10.1016/S0921-4526(99)00981-3

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  229. Charge-orbital stripe structure in La1-xCaxMnO3 (x=1/2, 2/3)

    Mutou T, Kontani H

    PHYSICAL REVIEW LETTERS   Vol. 83 ( 18 ) page: 3685 - 3688   1999.11

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    DOI: 10.1103/PhysRevLett.83.3685

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  230. Effects of spin fluctuations and superconductivity in quasi-one-dimensional organic conductors

    Kino H, Kontani H

    JOURNAL OF LOW TEMPERATURE PHYSICS   Vol. 117 ( 3-4 ) page: 317 - 321   1999.11

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    DOI: 10.1023/A:1022505330043

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  231. Hall effect and resistivity in high-Tc superconductors: The conserving approximation Reviewed

    H. Kontani, K. Kanki, and K. Ueda

    Physical Review B.   Vol. 59 ( 22 ) page: 14723-14739   1999.7

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    The Hall coefficient RH in high-Tc cuprates in the normal state shows the striking non-Fermi-liquid behavior: RH follows a Curie-Weiss type temperature dependence and |RH|≫1/|ne| at low temperatures in the underdoped compounds. Moreover, RH is positive for hole-doped compounds and negative for electron-doped ones, although each of them has a similar holelike Fermi surface. In this paper, we give the explanation of this long-standing problem from the standpoint of the nearly antiferromagnetic (AF) Fermi liquid. We consider seriously the vertex corrections for the current which are indispensable to satisfy the conservation laws, which are violated within the conventional Boltzmann transport approximation. The obtained total current Jk takes an enhanced value and is no longer perpendicular to the Fermi surface due to the strong AF fluctuations. By virtue of this mechanism, the anomalous behaviors of RH in high-Tc cuprates are naturally explained. Both the temperature and the (electron, hole) doping dependences of RH in high-Tc cuprates are reproduced well by numerical calculations based on the fluctuation-exchange approximation, applied to the single-band Hubbard model with a holelike Fermi surface. We also discuss the singular temperature dependence of RH in other nearly AF metals, e.g., V2O3, κ-BEDT-TTF organic superconductors, and heavy fermion systems close to the AF phase boundary.

  232. Hall effect and resistivity in high-T-c superconductors: The conserving approximation

    Kontani H, Kanki K, Ueda K

    PHYSICAL REVIEW B   Vol. 59 ( 22 ) page: 14723 - 14739   1999.6

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    DOI: 10.1103/PhysRevB.59.14723

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  233. Theory of Hall effect and electrical transport in high-T-c cuprates: Effects of antiferromagnetic spin fluctuations

    Kanki K, Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 68 ( 5 ) page: 1614 - 1624   1999.5

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    DOI: 10.1143/JPSJ.68.1614

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  234. Effects of spin fluctuations in quasi-one-dimensional organic superconductors

    Kino H, Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 68 ( 5 ) page: 1481 - 1484   1999.5

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    DOI: 10.1143/JPSJ.68.1481

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  235. Anomalous Hall effect in Sr2RuO4

    Miyazawa M, Kontani H, Yamada E

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 68 ( 5 ) page: 1625 - 1631   1999.5

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    DOI: 10.1143/JPSJ.68.1625

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  236. Phase diagram of superconductivity on the anisotropic triangular lattice Hubbard model: An effective model of kappa-(BEDT-TTF) salts

    Kino H, Kontani H

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 67 ( 11 ) page: 3691 - 3694   1998.11

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    DOI: 10.1143/JPSJ.67.3691

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  237. Phase Diagram of Superconductivity on the Anisotropic Triangular Lattice Hubbard Model: An Effective Model of κ-(BEDT-TTF) Salts Reviewed

    Hiori Kino and Hiroshi Kontani

    Journal of the Physical Society of Japan   Vol. 1998 ( 7 ) page: 3691-3694   1998.7

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    We study the electronic states of the anisotropic triangular lattice Hubbard model at half-filling, which is a simple effective model for the organic superconducting κ-BEDT-TTF compounds. We treat the effect of the Coulomb interaction by the fluctuation exchange (FLEX) method, and obtain the phase diagram of this model for various sets of parameters. It is shown that d-wave superconductivity is realized in a wide region of the phase diagram, next to the antiferromagnetic states. The obtained phase diagram explains well the characteristics of the experimental results.

  238. Electronic properties of the trellis-lattice Hubbard model: Pseudogap and superconductivity

    Kontani H, Ueda K

    PHYSICAL REVIEW LETTERS   Vol. 80 ( 25 ) page: 5619 - 5622   1998.6

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    DOI: 10.1103/PhysRevLett.80.5619

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  239. Theory of anomalous Hall effect in a heavy fermion system with a strong anisotropic crystal field

    Kontani H, Miyazawa M, Yamada K

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 66 ( 8 ) page: 2252 - 2255   1997.8

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    DOI: 10.1143/JPSJ.66.2252

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  240. Electronic state and magnetic susceptibility in orbitally degenerate (J=5/2) periodic Anderson model

    Kontani H, Yamada K

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 66 ( 8 ) page: 2232 - 2235   1997.8

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    DOI: 10.1143/JPSJ.66.2232

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  241. Quantum fluctuations and frustration of the collinear phase in CaV3O7

    Kontani H, Zhitomirsky ME, Ueda K

    PHYSICA B   Vol. 230   page: 752 - 755   1997.2

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    DOI: 10.1016/S0921-4526(96)00830-7

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  242. Plaquette resonating-valence-bond ground state of CaV4O9

    Ueda K, Troyer M, Kontani H, Sigrist M, Lee PA

    JOURNAL OF THE KOREAN PHYSICAL SOCIETY   Vol. 29   page: S128 - S130   1996.8

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  243. Plaquette resonating-valence-bond ground state of CaV4O9 (vol 76, pg 1932, 1996)

    Ueda K, Kontani H, Sigrist M, Lee PA

    PHYSICAL REVIEW LETTERS   Vol. 76 ( 24 ) page: 4650 - 4650   1996.6

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    DOI: 10.1103/PhysRevLett.76.4650

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  244. Effect of quantum fluctuations on magnetic ordering in CaV3O7

    Kontani H, Zhitomirsky ME, Ueda K

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 65 ( 6 ) page: 1566 - 1569   1996.6

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    DOI: 10.1143/JPSJ.65.1566

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  245. Phase diagram of depleted Heisenberg model for CaV4O9

    Troyer M, Kontani H, Ueda K

    PHYSICAL REVIEW LETTERS   Vol. 76 ( 20 ) page: 3822 - 3825   1996.5

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    DOI: 10.1103/PhysRevLett.76.3822

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  246. Plaquette resonating-valence-bond ground state of CaV4O9

    Ueda K, Kontani H, Sigrist M, Lee PA

    PHYSICAL REVIEW LETTERS   Vol. 76 ( 11 ) page: 1932 - 1935   1996.3

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    DOI: 10.1103/PhysRevLett.76.1932

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  247. Magnetic Susceptibility of the Orbitally Degenerate ( J = 5/2) Periodic Anderson Model - Analysis on the Basis of the Fermi Liquid Theory - Reviewed

    Hiroshi Kontani and Kosaku Yamada

    Journal of the Physical Society of Japan   Vol. 65 ( 1 ) page: 172-188   1996.1

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    In the orbitally degenerate (J= 5/2) Periodic Anderson Model, the magnetic susceptibility is composed of both the Pauli term and the Van Vleck term, as is well known. The former is strongly enhanced by the strong correlation between f-electrons. But, for the latter, the influence of the strong correlation has been obscure for years. In this paper we give the solution of the longstanding problem. With the aid of the d=∞ approximation, we study this problem on the basis of the Fermi liquid theory with degenerate orbitals, taking account of all the vertex corrections in a consistent way. As a result, we obtain the simple expression for the magnetic susceptibility, and show unambiguously that the Van Vleck term is also highly enhanced in the strong correlation regime. This fact explains naturally the enhanced magnetic susceptibility observed in many insulating systems (i.e., Kondo insulator). Moreover, we show that the Wilson ratio takes a value around 1 in the metallic system, in good agreement with experiments.

  248. Plaquette resonating-valence-bond ground state of CaV4O9

    Kontani H, Troyer M, Ueda K, Sigrist M, Lee PA

    CZECHOSLOVAK JOURNAL OF PHYSICS   Vol. 46   page: 1903 - 1904   1996

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    DOI: 10.1007/BF02570943

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  249. Theory of Anomalous Hall Effect in Heavy Fermion System Reviewed

    Hiroshi Kontani and Kosaku Yamada

    Journal of the Physical Society of Japan   Vol. 1994 ( 7 ) page: 2627-2652   1994.7

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    The theory of the anomalous Hall effect in the heavy fermion system in the coherent regime is developed on the basis of the periodic Anderson Hamiltonian with degenerate orbitals. The anomalous Hall conductivity arises from the skew-scattering due to the orbital momenta of f-electrons in the presence of magnetic field. By a newly developed analysis based on the phase factor of the f-electron wavefunction in x-y plane, a simple expression for the Hall conductivity σ xy is derived. It makes possible to understand clearly the mechanism and to estimate the sign and the magnitude of the anomalous Hall coefficient. Our theory explains well experimental results in the heavy fermion systems. Finally, we discuss the extension of this theory to explain the temperature dependence of the Hall coefficient in the cuprate high-T c superconductors.

  250. ANOMALOUS HALL-COEFFICIENT IN HEAVY-ELECTRON SYSTEMS

    YAMADA K, KONTANI H, KOHNO H, INAGAKI S

    PROGRESS OF THEORETICAL PHYSICS   Vol. 89 ( 6 ) page: 1155 - 1166   1993.6

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    DOI: 10.1143/PTP.89.1155

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▼display all

Books 1

  1. Transport Phenomena in Strongly Correlated Fermi Liquids (Springer Tracts in Modern Physics)

    Hiroshi Kontani( Role: Sole author)

    Springer  2013.4 

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    Language:English

Presentations 1

  1. Even- and Odd-Parity Density Waves and Superconductivity in Kagome Metals and Other Strongly Correlated Metals Invited

    Hiroshi Kontani

    Superstripes 2023  2023.6.30 

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    Event date: 2023.6 - 2023.7

    Language:English   Presentation type:Oral presentation (keynote)  

    Venue:Ischia-Naples   Country:Italy  

    Other Link: https://www.superstripes.net/conferences/superstripes-2023

Research Project for Joint Research, Competitive Funding, etc. 3

  1. 鉄ニクタイド系化合物超伝導体の微視的・非経験的理論研究

    2008.10 - 2012.3

    特色ある大学教育支援プログラム 

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    Grant type:Competitive

  2. 鉄ニクタイド系化合物超伝導体の微視的・非経験的理論研究

    2008.10 - 2012.3

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    第一原理電子状態計算、多体モデル計算の専門家を結集し、それぞれの得意とするアプローチを有機的かつ複合的に組み合わせて、微視的な立場から鉄ニクタイド系化合物の本質を明らかにすべく、以下の課題に取り組みます。
    (1)精密な計算による超伝導機構の解明
    (2)ギャップ関数の対称性や構造などの超伝導特性の解析
    (3)磁性、輸送特性などの常伝導状態の諸物性の解析
    (4)界面・接合系での輸送特性の解析
    (5)新しい方法による電子状態計算、微視的有効模型の第一原理的構築
    (6)新結晶構造、新物質群の探索。特に、より高い転移温度の実現を目指す物質設計
     非経験的な計算をベースにできるだけ現実に即した計算を実行し、実験グループとの連携を密に取りながら、既存の実験事実の解明のみにとどまらず、新概念の創出、新物質の設計を積極的に行うことを目標とします。

  3. 非一様な強相関電子系における電子状態、特に輸送現象の理論的研究

    2006

KAKENHI (Grants-in-Aid for Scientific Research) 28

  1. Physical Properties of Quantum Liquid Crystals

    Grant number:19H05822  2019.6 - 2024.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

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    Authorship:Coinvestigator(s) 

  2. 量子液晶の理論構築

    Grant number:19H05825  2019.6 - 2024.3

    科学研究費助成事業  新学術領域研究(研究領域提案型)

    紺谷 浩, 求 幸年, 遠山 貴巳, SHANNON Nic, 有田 亮太郎, 池田 浩章, 佐藤 正寛

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    Authorship:Principal investigator 

    Grant amount:\163020000 ( Direct Cost: \125400000 、 Indirect Cost:\37620000 )

    近年、ナノからメゾスケールの自己組織化を伴う量子液晶状態が、様々な電子系で相次いで発見された。例えば鉄系および銅酸化物超伝導体では電荷液晶が、量子スピン系ではスピン液晶が実現する。そこで本研究では、各分野で独立に発展してきた理論手法を糾合して、多彩な量子液晶の根底にある普遍的な原理を解明する。量子液晶状態におけるマヨラナ粒子などの新種の素励起(固体中の新素粒子)や、エキゾティック超伝導など液晶揺らぎによる創発現象を研究する。また量子液晶に対する制御理論や非平衡現象の理論を発展させる。同時に第一原理的手法を駆使して、量子液晶状態を実現する物質設計の理論を構築する。
    強相関電子系において普遍的に観測される、ナノからメゾスケールの自己組織化を伴う量子液晶状態に対する理論研究を推進し、以下の研究実績をあげた。
    電荷液晶に関する研究実績では、鉄系超伝導体および銅酸化物超伝導体における、新種の電荷ネマティック秩序やスメクティック秩序を理論的に予言し、実験班による実験報告に対する理論的説明を与えた。遷移金属ダイカルコゲナイドにおける非整合電荷秩序の微視的起源を説明した。また、新規強相関超伝導体であるニッケル酸化物超伝導体の理論研究を実施し、この系の多体電子状態および超伝導発現機構を、第一原理的手法に基づき明らかにした。更に、動的密度行列繰り込み群法などの最先端の理論手法を駆使して、量子液晶の非平衡現象やダイナミクスの理論を構築した。
    さらに第一原理的手法を駆使して、超高圧下の高温超伝導体LaH10の理論研究を推進した。その結果、この系の新奇な圧力誘起量子液体状態が明らかになり、この系の高温超伝導発現機構に関する重要な知見を得ることが出来た。
    スピン液晶に関する研究実績では、モアレスピン超格子の概念を導入し、各種スピン液晶に対する包括的議論を行った。並行して、様々な大規模数値解析手法を糾合して各種スピン系を詳細に調べ、その基底状態や励起状態、創発的電磁現象を明らかにした。またキタエフスピン系など代表的な量子スピン系におけるスピン液体状態や励起状態、各種輸送現象の理論研究を行い、実験班との協力により重要な成果を上げた。
    量子液晶現象が発現する代表的物質であり、世界的に研究が進展している鉄系超伝導体や銅酸化物高温超伝導体(電荷液晶)、フラストレート量子スピン系やキタエフスピン系(スピン液晶)の理論研究において、重要な研究の進展が得られた。例えば、鉄検超伝導体におけるスメクティック秩序の理論を新たに提唱し、実験班による実験報告の理解を可能にした。また量子スピン系における熱伝導など各種輸送現象について、実験班と協力して研究を推進し、著しい進展が得られた。
    加えて、量子液晶状態の数値的計算手法に関して、重要な進歩があった。例えば、電荷液晶の秩序パラメーターを「構造因子」として一般化し、汎関数繰り込み群理論や密度波方程式理論に基づいて構造因子の最適化を行うことで、量子液晶秩序をバイアスなく決定する手法が開発された。また、モアレスピン超格子の概念を導入することで、スピン液晶の多様性や創発的電磁現象に関する包括的な研究が可能になった。更に、第一原理計算手法に基づく量子液晶物質の物質設計の理論においても、大きな進展があった。今回開発された理論計算手法を、様々な量子液晶物質に適用することにより、重要な研究成果が見込まれる。
    上記の理由より、現在までの研究の進捗状況は、大変順調に進展していると判断される。
    今後の研究の推進方策は以下の通りである。
    〇電子液晶の研究: 本班で発展させてきた汎関数繰り込み群理論や密度波方程式、動的平均場理論といった最先端の量子多体理論に基づき、様々な強相関金属を網羅的に解析し、新しい電荷液晶秩序を予言する。また群論に基づく現象理論を発展させ、電子液晶における新種の電気磁気効果や非線形現象、非相反現象を解明する。
    〇スピン液晶の研究: 本班で発展させてきたマヨラナ平均場近似法や量子モンテカルロ法などの理論的手法を活用し、キタエフスピン系をはじめとする様々な量子スピン液体系におけるスピン液晶秩序の研究を推進する。加えて多項式展開ランジュバン法などの計算手法を用いて、磁気スキルミオンなど磁気テクスチャや量子輸送現象の研究を行う。
    〇量子液晶の非平衡現象: 動的密度行列繰り込み群法などの大規模数値計算を推進し、量子液晶における動的性質を研究する。また、スピン流揺らぎやレーザー駆動高次高調波の解析を推進する。
    〇非従来型超伝導の発現機構の研究: 超高圧下の高温超伝導体LaH10やニッケル酸化物超伝導体、STO基板上のFeSeなどの非従来型の高温超伝導の発現機構を解明する。量子液晶の揺らぎが媒介する新規引力機構を考慮して、従来のMigdal-Eliashberg理論を超えた多体効果(バーテックス補正)を考慮した超伝導理論を構築する。
    〇量子液晶の総合的研究: これまで本班で培ってきた、電荷液晶、スピン液晶、電子対液晶に関する理論的知見を糾合し、量子液晶の統一的理論の構築を目指した総合的研究を推進する。

  3. 電子相関が創出する電子液晶現象の理論:素励起、超伝導および量子臨界現象

    Grant number:18H01175  2018.4 - 2021.3

    科学研究費助成事業  基盤研究(B)

    紺谷 浩, 土射津 昌久

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    Authorship:Principal investigator 

    Grant amount:\17030000 ( Direct Cost: \13100000 、 Indirect Cost:\3930000 )

    鉄系超伝導体や銅酸化物超伝導体、重い電子系に対して多体電子状態の理論研究を実施し、以下の新規多体効果を新たに見出した。
    鉄系超伝導体の研究: 過剰電子ドープ系において発見された新種の電子ネマティク秩序である「B2gネマティック秩序」に対する理論解明を行った。その秩序変数は鉄のd_{xy}軌道を舞台とするC4対称性の破れである「d波ボンド秩序」である。その微視的起源はスピン揺らぎ間の量子干渉効果であり、Aslamazov-Larkin型ダイヤグラムで記述される。また、鉄系超伝導体の超伝導状態(T<Tc)における動的スピン帯磁率を精度よく計算する手法を開発し、非弾性中性子散乱実験で観測される「レゾナンスピーク」がS++波状態に基づき定量的に説明可能であることを見出した。本理論では、従来の理論で無視されていた自己エネルギー補正が本質的役割を果たす。
    銅酸化物超伝導体の研究: (1,1)エッジの表面においてアンドレーフ束縛状態に由来する強磁性臨界現象を見出した。特に、強磁性揺らぎが媒介する「エッジ誘起p波超伝導」の発現を理論的に見出した。
    重い電子系の研究: f軌道の強いスピン軌道相互作用がもたらす「多極子自由度」に注目し、f電子系の多極子揺らぎ理論を構築した。Aslamazov-Larkinバーテックス補正を考慮することで、磁気多極子揺らぎ間の干渉効果によって電気多極子秩序が生じる新機構を明らかにした。この機構を用いて、「CeB6における四極子秩序」や「CeCu2Si2における十六極子揺らぎs波超伝導機構」を理論的に導出した。
    鉄系超伝導体の研究においては、過剰電子ドープ系における「B2gネマティック秩序」に対する理論解明を、世界に先駆けて行うことが出来た。その微視的起源である「量子干渉効果」は、我々のグループが世界に先駆けて明らかにした電子相関機構であり、明確なオリジナリティーが認められる。また、非弾性中性子散乱実験における「レゾナンスピーク」をS++波状態に基づく定量的説明に成功し、これによりこの系の超伝導対称性に関する大変重要な知見を得ることが出来た。
    銅酸化物超伝導体の研究では、アンドレーフ束縛状態に由来するエッジ強磁性臨界現象を初めて明らかにすることが出来た。
    重い電子系の研究においては、Aslamazov-Larkinバーテックス補正を考慮した「f電子系の多極子揺らぎ理論」を、本研究により初めて構築することが出来た、その結果、磁気多極子揺らぎ間の干渉効果によって田財な電気多極子秩序が生じる新機構を明らかになった。本理論に基づき、「CeB6における四極子秩序」や「CeCu2Si2における十六極子揺らぎs波超伝導機構」などの、f電子系の重要未解明問題を説明することが出来た。
    以上の研究業績を考慮し、現在までの進捗状況は十分順調に進展していると判断した。
    鉄系超伝導体や銅酸化物超伝導体、重い電子系をはじめとする、様々な強相関金属を総合的に解析する。バーテックス補正を考慮した多体電子状態の理論研究を推進し、以下の理論研究を推進する。
    新規強相関電子系の解析: 遷移金属ダイカルコゲナイドや捻り2層グラフェン、カゴメ格子系などの新しい強相関金属を研究する。特に、これらの電子系で発現する新奇な量子相転移(ネマティック秩序やスメクティック秩序など)について、Aslamazov-Larkin型バーテックス補正を考慮した理論解析を実行する。
    新規超伝導体の超伝導発現機構の研究: 最近実験的に明らかにされた、鉄系超伝導体Fe(Se,Te)の状態相図によると、この系の超伝導機構は電子ネマティク揺らぎが担っている可能性が高い。この実験事実に着目して、電子ネマティク揺らぎが媒介するS波超伝導の理論を構築する。本理論をFe(Se,Te)をはじめとする様々な鉄系超伝導体や、各種新規超伝導体に適用し、未知の超伝導発現機構を研究する。
    新規多体理論の構築: 平均場近似を超えた高次多体効果を計算する手法として、汎関数繰り込み群法(fRG)は大変有力である。最近我々は、fRGに基づき量子液晶秩序の秩序変数である「構造因子」をバイアスなく決定する手法を開発し、擬一次元電子系において「電流ループ秩序」が生じることを明らかにした。この理論をさらに発展させて、各種2次元電子系に適用し、電子相関による量子相転移現象をバイアスなく研究する。

  4. 電子相関が創出する電子液晶現象の理論:素励起、超伝導および量子臨界現象

    2018.4 - 2020.3

    科学研究費補助金  基盤研究(B)

    紺谷浩

  5. 強相関超伝導体における電荷・軌道・スピン複合自由度の協奏現象の理論解明

    2015.4 - 2018.3

    科学研究費補助金  基盤研究(B)

    紺谷浩

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    FeSe における磁性を伴わない液晶秩序を説明すべく、バーテックス補正の理論に立脚してFeSe の相図の包括的理解を行った。特に、(1)TS 以下の波数空間における符号反転を伴う軌道秩序、(2)圧力誘起磁性秩序およびTS の増大、(3)原子層FeSe における高温s++波超伝導の発現機構を研究した。また、銅酸化物超伝導体における電荷液晶を研究し、その正体が多体効果による有効hopping の対称性が破れたd波ボンド秩序であることを見出した。

  6. Novel cooperative phenomena among charge, spin, and orbital degrees of freedoms in strongly correlated electron systems

    Grant number:15H03687  2015.4 - 2018.3

    Hiroshi Kontani

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    Grant amount:\16900000 ( Direct Cost: \13000000 、 Indirect Cost:\3900000 )

    In strongly correlated electron systems, impact of vertex corrections (VCs), which describes the higher-order many-body effects, attract increasing attention. Here, we perform the theoretical study of VCs in Fe-based and cuprate superconductors, based on both the diagrammatic method and functional RG method. We revealed that the “electronic nematic states” observed in these strongly correlated systems, originate from the Aslamazov-Larkin VCs. The physical meaning of the Aslamazov-Larkin VCs is the “quantum interference between charge, spin, and orbital fluctuations”, which is found to be very important in various strongly correlated electron systems.

  7. Novel orbital physics and mechanism of superconductivity in Fe-based superconductors

    Grant number:24340081  2012.4 - 2016.3

    Kontani Hiroshi

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    Authorship:Principal investigator 

    Grant amount:\19110000 ( Direct Cost: \14700000 、 Indirect Cost:\4410000 )

    We studied (i) the origin of the C2-symmetric electronic nematic order and (ii) the mechanism of high-Tc superconductivity in Fe-based superconductors. The nematic order cannot be explained within the mean-field-type approximations. However, we revealed that the orbital order originates from the vertex correction, which represents the mode-coupling between orbital and spin fluctuations. Therefore, the nematic order in Fe-based superconductors is satisfactorily explained as the C2-symmetric electronic state due to the orbital order. By analyzing the vertex correction, the nematic order without magnetization in FeSe has been explained satisfactorily. In addition, we revealed that the orbital fluctuations give the strong pairing interaction that accounts for high-Tc superconductivity.

  8. 鉄系超伝導体の新規な多軌道物理現象と超伝導発現機構

    2012.4 - 2015.3

    科学研究費補助金  基盤研究(B)

    紺谷浩

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    鉄系超伝導体における軌道秩序の出現は、超伝導発現機構と密接に関係した重要な事実である。本研究では高次の電子相関効果である「バーテックス補正」を考慮した理論を構築し、多軌道ハバード模型に適用することで、平均場レベルの理論では説明できなかった鉄系超伝導体の相図の再現に世界で初めて成功した。さらに、スピン揺らぎと軌道揺らぎが共存する場合に期待される「s++波状態とs±波状態のクロスオーバー」に関する先駆的な理論計算を行い、ARPES 等の実験事実の説明に成功した。更に、バーテックス補正の理論を銅酸化物に適用し、平均場レベルの理論で説明ができなかったQ=(π/2,0)ストライプ電荷秩序の再現に、世界に先駆けて成功した。

  9. Novel Transport Phenomena due to Orbital Degree of Freedoms

    Grant number:21540358  2009 - 2011

    KONTANI Hiroshi

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    Authorship:Principal investigator 

    Grant amount:\4290000 ( Direct Cost: \3300000 、 Indirect Cost:\990000 )

    We studied the many-body electronic states in metals with orbital degree of freedoms. The main objects are (i) spin Hall effect and anomalous Hall effect driven by the Berry phase due to orbital degree of freedoms and spin-orbit coupling (orbital Berry phase), and (ii) the mechanism of superconductivity and anomalous transport phenomena due to orbital fluctuations driven by Coulomb interaction.

  10. 重い電子系の形成と秩序化

    2008.4 - 2013.3

    科学研究費補助金  新学術領域研究

    上田和夫

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    我々はf電子系における非フェルミ液体的輸送現象を、バーテックス補正を考慮した解析により説明を行った。さらに、f電子不純物によるスキュー散乱により、巨大スピンホール効果が発現することを世界に先駆けて見出した。一連の研究で発展させた多重極相互作用の理論的取り扱い手法を発展させて、強相関電子系における軌道揺らぎ理論の構築に成功した。

  11. フラストレート系における輸送現象、特にホール効果の理論研究

    2008.4 - 2010.3

    科学研究費補助金  特定領域研究

    紺谷 浩

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    Authorship:Principal investigator 

    パイロクロア結晶構造を持つ遍歴強磁性金属Nd2Mo2O7における非従来型異常ホール効果について研究し、そのメカニズムを解明した。この物質では、低温でNdサイトの局在f電子がスピンアイス秩序と呼ばれる互いに傾いたスピン配置を示し、d-f交換相互作用の結果、金属伝導を担うMoの4d電子のスピンが角度θだけ傾いた「傾いた強磁性状態」が実現する。このとき出現する顕著な異常ホール効果は、巨視的磁化に比例する従来型の異常ホール効果では到底説明できず、「微視的スピン構造がもたらす非従来型里常ホール効果」として注目を集めてきた。その起源として、スピンカイラリティー機構が提唱されて注目を集めたが、実験の定量的説明には至らなかった。
    その説明として、申請者は軌道Aharonov-Bohm効果の理論を提唱した[T.Tomizawa and H.Kontani. Phvs. Rev. B 80, 100401(R) (2009) ; Editor's suggestion]。軌道自由度を考慮すると、カゴメ格子上の三角形の経路を電子が一周する際に、各Moサイ下で原子軌道の位相差に由来する、θに比例するベリー位相因子を獲得することがわかる。このベリー位相は、経路中を貫ぬく有効磁場の働き昂するため、雷子は外部電場と垂直方向にドリフト運動する。その結果、θに線形め顕著な異常ホール効果が出現ずる。Nd2Mo2O7ではθ≪1であるごとから、スピンカイラリティー機構よりも軌道機構が重要である。このようにして、10年来の謎であったNd2Mo2O7における非従来型異常ホール効果は、申請者の提唱する軌道機構として定量的に理解できることが明らかになった。

  12. Theory of exotic quantum order and novel superconductivity emerging from multi degrees of freedom of f electron

    Grant number:20102008  2008 - 2012

    Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

    HOTTA Takashi

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    Heavy electron phenomena emerge in rare-earth and actinide compounds, when f electron exhibits huge effective mass which is a few hundred or thousand times as large as the bare electron mass. Thus far, the heavy electron state has been understood by the competition between itinerant and localized nature of f electron. In this research, we have clarified new heavy-electron mechanisms due to multi degrees of freedom such as f-electron orbital and phonon in addition to spin and charge. We have also developed the theory of ordering of multipole as spin-orbital complex, quantum criticality due to valence fluctuations, superconductivity due to anharmonic phonons, and orbital-fluctuation-induced superconductivity in orbital degenerate systems.

  13. Verification of the giant spin Hall effect in heavy Fermion systems and application to spintronics

    Grant number:20246004  2008 - 2010

    TERASHIMA Takahito

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    Spin Hall effect, a phenomena to produce a magnetized state by flowing electric current along the narrow wire, is expected to develop new spintronic devices. We have investigated the development of new rare earth based material systems experimentally and theoretically to realize spin-Hall effect devices. Thin films and artificial superstructures of rare earth based intermetallic compounds which are expected to exhibit large spin Hall effects were fabricated for the first time.

  14. フラストレート系における輸送現象、特にホール効果の理論研究

    Grant number:20046007  2008 - 2009

    紺谷 浩

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    Grant amount:\1700000 ( Direct Cost: \1700000 )

    パイロクロア結晶構造を持つ遍歴強磁性金属Nd2Mo2O7における非従来型異常ホール効果について研究し、そのメカニズムを解明した。この物質では、低温でNdサイトの局在f電子がスピンアイス秩序と呼ばれる互いに傾いたスピン配置を示し、d-f交換相互作用の結果、金属伝導を担うMoの4d電子のスピンが角度θだけ傾いた「傾いた強磁性状態」が実現する。このとき出現する顕著な異常ホール効果は、巨視的磁化に比例する従来型の異常ホール効果では到底説明できず、「微視的スピン構造がもたらす非従来型里常ホール効果」として注目を集めてきた。その起源として、スピンカイラリティー機構が提唱されて注目を集めたが、実験の定量的説明には至らなかった。
    その説明として、申請者は軌道Aharonov-Bohm効果の理論を提唱した[T.Tomizawa and H.Kontani. Phvs. Rev. B 80, 100401(R) (2009) ; Editor's suggestion]。軌道自由度を考慮すると、カゴメ格子上の三角形の経路を電子が一周する際に、各Moサイ下で原子軌道の位相差に由来する、θに比例するベリー位相因子を獲得することがわかる。このベリー位相は、経路中を貫ぬく有効磁場の働き昂するため、雷子は外部電場と垂直方向にドリフト運動する。その結果、θに線形め顕著な異常ホール効果が出現ずる。Nd2Mo2O7ではθ≪1であるごとから、スピンカイラリティー機構よりも軌道機構が重要である。このようにして、10年来の謎であったNd2Mo2O7における非従来型異常ホール効果は、申請者の提唱する軌道機構として定量的に理解できることが明らかになった。

  15. 相互作用の拮抗がもたらす超伝導現象、輸送現象および不純物効果の理論研究

    2007.4 - 2009.3

    科学研究費補助金  特定領域研究

    紺谷 浩

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    鉄砒素系超伝導体における超伝導状態は、一般の異方的超伝導体と異なり、不純物や乱れに対してかなり強いことが実験で明らかにされた。この実験事実は、超伝導ギャップの符号変化が存在しないことを示唆し、RPA近似等が予言する符号反転s波状態(s±波状態)と一見矛盾する。そこで我々はs±波状態に対する不純物効果を明らかにする目的で、2バンドBCS模型を詳細に解析した。鉄砒素系のように各バンドの軌道成分が異なる時、バンド内不純物散乱ポテンシャルIとバンド間不純物散乱ポテンシャルI'は異なる(I'/I≠1)ことがわかる。我々の解析によると、I≫N(0)のユニタリー領域においては、I'/I=1という特殊な場合に限り顕著な対破壊効果が生じ、わずか1~2%の不純物によってTc(~50K)が消滅するが、一般には対破壊効果は非常に小さく、10%以上の不純物濃度でもTcが有限に残ることを明らかにした。その理由は、多重散乱をT行列で無限次まで足し上げる結果、I'/I≠1の場合にはバンド間散乱が繰り込まれて小さくなるためである。本研究により不純物効果の実験事実は、現実的5バンド模型に基づき理論的に予言されるs±波状態と矛盾しないことが明らかになった。

  16. Theory of spin injection and accumulation in nano-hetero structures

    Grant number:19048022  2007 - 2010

    INOUE Junichiro

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    Electrons have two degrees of freedom, charge and spin. The former is the basis of semiconductor electronics, and the latter is the origin of magnetism and applied to magnets. In normal metals and semiconductors, the spin angular momentum is zero in average, but in ferromagnets, it is non-zero. As a consequence, the current in a ferromagnet has a flow of spins (spin current). In the present research, we have shown that the novel phenomenon called spin Hall effect becomes large in metals. We also have shown that the spin current can be created by current in ferromagnet /semiconductor (graphene) junctions, and that the effect of magnetic field on the current is large in these junctions. The result indicates an applicability of these junctions to novel devices.

  17. 相互作用の拮抗がもたらす超伝導現象、輸送現象および不純物効果の理論研究

    Grant number:19014008  2007 - 2008

    紺谷 浩

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    Grant amount:\1800000 ( Direct Cost: \1800000 )

    鉄砒素系超伝導体における超伝導状態は、一般の異方的超伝導体と異なり、不純物や乱れに対してかなり強いことが実験で明らかにされた。この実験事実は、超伝導ギャップの符号変化が存在しないことを示唆し、RPA近似等が予言する符号反転s波状態(s±波状態)と一見矛盾する。そこで我々はs±波状態に対する不純物効果を明らかにする目的で、2バンドBCS模型を詳細に解析した。鉄砒素系のように各バンドの軌道成分が異なる時、バンド内不純物散乱ポテンシャルIとバンド間不純物散乱ポテンシャルI'は異なる(I'/I≠1)ことがわかる。我々の解析によると、I≫N(0)のユニタリー領域においては、I'/I=1という特殊な場合に限り顕著な対破壊効果が生じ、わずか1~2%の不純物によってTc(~50K)が消滅するが、一般には対破壊効果は非常に小さく、10%以上の不純物濃度でもTcが有限に残ることを明らかにした。その理由は、多重散乱をT行列で無限次まで足し上げる結果、I'/I≠1の場合にはバンド間散乱が繰り込まれて小さくなるためである。本研究により不純物効果の実験事実は、現実的5バンド模型に基づき理論的に予言されるs±波状態と矛盾しないことが明らかになった。

  18. 非一様な強相関電子系における電子状態、特に輸送現象の理論的研究

    2006.4 - 2009.3

    科学研究費補助金  若手研究(B)

    紺谷浩

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    反強磁性量子臨界点(AF-QCP)近傍の強相関電子系では、わずか1%の非磁性不純物が系全体の電子状態を劇的に変化させることが知られている。たとえば銅酸化物高温超伝導体では、1%のZn不純物により巨大な残留抵抗が生じたり、1μBに達する大きな局在モーメントが発生する。今回我々は、FLEX近似を拡張して空間的に非一様な状態に適用できる近似理論(GVI理論)を開発して、高温超伝導体における非磁性不純物問題を解析した。その結果、上記の実験事実を第一原理的に再現することに始めて成功した。その後、我々は鉄砒素系高温超伝導体における不純物効果を研究し、超伝導対称性に関する重要な知見を得た。さらに我々はAg金属中におけるYb不純物が、Ybの電子相関によって劇的に大きなスピンホール効果をもたらすことを理論的に予言した。

  19. Theoretical study of electronic states and transport phenomena in inmohogeneous strongly correlated electron systems

    Grant number:18740197  2006 - 2008

    KONTANI Hiroshi

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    Grant amount:\3800000 ( Direct Cost: \3500000 、 Indirect Cost:\300000 )

  20. 充填スクッテルダイト化合物が示す特徴的物性の理論的解明

    Grant number:18027004  2006 - 2007

    倉本 義夫

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    理論班は,スクッテルダイト系における新奇現象理解への鍵となる概念形成を行い,全計画班の連携をサポートすることなどを主要な目標として活動した。その結果,以下を例とする多くの成果を得た。
    1. Prスタッテルダイトでは,結晶場状態により,近藤効果の重要性が大きく異なることを微視的な計算によって示した。
    2. PrFe4P12やPrRu4P12の秩序変数は,結晶の立方対称性を保つスカラー型であり,これが交替的に副格子を形成していることを提案し,温度に依存する結晶場状態など多くの実験を説明した。
    3. SmRu4P12の奇妙な相図と物性について,磁気八極子が主要な秩序変数であることを確認し,CeB6との類似性から特徴的なNQRパターンなどを説明できることを指摘した。
    4.多極子秩序による帯磁率,磁気異方性への反映を現象論を用いて明らかにした。これにより実験結果を多極子の描像によって合理的に解釈した。
    5. PrFe4P12の複雑な核磁気共鳴スペクトルを対称性を考慮して解析し,スカラー型秩序変数の描像で説明できることを示した。
    6.伝導電子のバンド構造が秩序構造に与える役割を明らかにした。特に結晶構造とリガンド電子の構造により強いネスティングが存在することが,多極子の反強的秩序形成に重要であることを示した。
    7.スクッテルダイト特有の構造によるラトリングの役割に注目し,超音波物性に対する特有の効果を明らかにした。また磁場に鈍感な重い電子生成に導く可能性を指摘した。

  21. スクッテルダイト化合物における重い電子状態と近藤絶縁体状態の理論

    Grant number:16037204  2004 - 2005

    佐宗 哲郎

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    1.Ce-スクッテルダイト化合物のうちの,CeRu_4Sb_<12>については,バンド計算では絶縁体だが,実験では金属で,矛盾していた。そこで,昨年度に構築したtight-binding模型を改良し,さらに本質的な部分のみを抽出した模型を新たに作った。これは,実験と合う半金属型の模型である。これを用いて,電気抵抗・熱起電力(Seebeck係数)・光学伝導度の計算を行い,半定量的に実験結果を説明することに成功した。(論文印刷中)
    2.おなじく,CeOs_4Sb_<12>について,実験で,温度0.8Kでスピン密度波への転移が見つかっており,しかも,磁場をかけると転移温度が上昇するという特異な振る舞いを示した。我々は,1.と類似の模型を用い,分子場近似により,この現象を説明することに成功した。(論文発表済)
    3.強相関電子系における光学伝導度およびホール伝導度の研究:通常金属における交流ホール係数は、R_H(ω)の虚部は殆ど0であり、これはボルツマン近似がよく成り立っていることを意味する。ところが高温超伝導体ではImR_H(ω)は有限のωで極めて大きな値をとり、その値は低温かつ低ドープ領域において非常に大きくなる。我々はR_H(ω)をFLEX近似に基づき、カレントに対するバーテックス補正をω依存性まで考慮して解析し、実験で観測される交流ホール係数の異常な振舞いを良く再現することが出来た。本研究により、高温超伝導体の交流及び直流輸送現象の振舞いが、フェルミ液体の立場からバーテックス補正を考慮することで「統一的に」理解できることが明らかになり、高温超伝導体の正常状態における電子状態の理解が進歩したといえる。(論文発表済)
    4.Na_<0.35>CoO_2についても,理論的な解析を行った。(論文発表済)

  22. 分子性導体の極限環境下における半導体から金属へのクロスオーバー

    Grant number:15073213  2003 - 2007

    鈴村 順三

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    本研究では。低次元電子系における、圧力下での絶縁体から金属までの伝導電子の状態変化に関して以下の研究を行った。1、擬一次元電子系において鎖間の異なる2つの電荷移動の競合が増加することによりモット絶縁体から金属へ移ることをN鎖繰り込み群を用いて明らかにし、この結果出現する金属状態はネスティングを反映しファルミ面に依存した準粒子であることを示した。2、1次元朝永-ラッチンジャー液体における境界効果を調べるために核磁気緩和率を計算した。境界から離れるとフェルミ波数に依存し振動しながら一定値に近づくこと、その振幅は相互作用により増加する一方、温度揺らぎにより減少するという両者の競合の振る舞いを明らかにした。3、擬2次元有機導体β"-(DODHT)_2PF_6は常圧では電荷秩序を示すが、圧力下では超伝導が出現する。これは圧力下で金属状態になりためで、この発現機構として電荷秩序が存在するか又は融解するかによりスピン揺らぎ又は電荷揺らぎの可能性を指摘した。4、1次元電子系(EDO-TTF)_2PF_4塩の特異な絶縁体を理解するため、斥力相互作用や格子歪との結合が存在する場合の電子系を調べ、最近接斥力が十分大きい場合に電子-格子相互作用の効果により特異なパイエルス状態が生じることを示した。さらに格子歪がゼロの近傍の準安定状態が光誘起伝導に寄与する可能性を指摘した。5、擬2次元有機導体α-(BEDT-TTF)_2I_3のゼロギャップ状態における密度波形成をしらべ、運動量空間の2つの縮退点を結ぶ波数を持つスピン密度波が、バンド間励起、相互作用及び3次元効果により出現する可能性を示した。

  23. 高温超伝導体やその関連物質における静的及び動的輸送現象の理論的研究

    Grant number:15740198  2003 - 2005

    紺谷 浩

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    Authorship:Principal investigator 

    Grant amount:\3500000 ( Direct Cost: \3500000 )

    ●強相関電子系における光学伝導度およびホール伝導度の研究:
    高温超伝導体における交流ホール係数は、ImR_H(ω)が有限のωで極めて大きな値をとり、更にその値は低温かつ低ドープ領域において非常に大きくなる。これはボルツマン近似の破綻を意味する。我々はR_H(ω)をFLEX近似に基づき、カレントに対するバーテックス補正をω依存性までまじめに考慮して解析した。この数値計算の手法は、本研究ではじめて開発されたものである。研究の結果、反強磁性近傍の金属では、バーテックス補正によりR_H(ω)の異常なωおよび温度依存性が良く再現されることが明らかになった。本研究により、高温超伝導体の交流及び直流輸送現象の振舞いが、フェルミ液体の立場からバーテックス補正を考慮することで「統一的に」理解できることが明らかになり、高温超伝導体おける電子状態および超伝導発現機構の理解が進んだといえる。
    ●三角格子Co酸化物超伝導体NaxCoO2・yH2Oの研究:
    水をインターカレートした超伝導体RaxCoO2・yH2Oにおける電子状態および超伝導発現機構を研究した。この系のフェルミ面は、バンド計算による予想とARPESによる実験結果とで大きく異なり、問題になっていた。そこで我々はFLEX近似に基づきNaxCoO2の正常状態を詳細に解析して、実験において観測されている帯磁率や状態密度の弱い擬ギャップ的振る舞いが、ARPESのフェルミ面を仮定した場合に限って再現できることを示した。次に我々は、CoO2層の光学フォノン(シェアモード、ブリージングモード)によるs波超伝導の可能性を考えた。解析の結果、シェアモードフォノンによって、クーパー対がFermi面を形成するalg軌道と価電子バンドを形成するeg'軌道の間を遷移するため、超伝導転移温度学が劇的に上昇することを明らかにした。この機構を我々はValence-Band Suhl-Kond機構と命名した。この機構に基づき、ARPESで観測されている準粒子スペクトルにおけるキンク構造も同時に再現できた。

  24. 高温超伝導体・有機物超伝導体の各種輸送現象における非フェルミ液体的挙動の理論

    Grant number:13740202  2001 - 2002

    紺谷 浩

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    Grant amount:\2400000 ( Direct Cost: \2400000 )

    1.高温超伝導体の擬ギャップ領域における輸送現象の理論:高温超伝導体の低ドープ領域では擬ギャップ温度T^*以下で各種物理量が擬ギャップ的振舞いを示し、そのメカニズムの解明は最近の高温超伝導体の研究における中心的課題である。最近Stanford大学のOng達により、高温超伝導体の常伝導相におけるネルンスト係数が詳細に計測され、擬ギャップ領域でネルンスト係数が著しく増大するという、通常の金属では考えられない特異な挙動を示すことが明らかになった。この実験結果から、Ong達は擬ギャップ領域で多数のボルテックス・反ボルテックス対が熱的に励起されていると考え、議論を呼んだ。一方、我々は擬ギャップ領域で強い超伝導揺らぎが発達しているという立場に立ち、フェルミ液体論の立場からネルンスト係数の計算を行った。その結果、カレントに対する多体効果であるバーテックス補正項を考慮することで、T^*以下におけるネルンスト係数及び磁気抵抗の急激な増大が再現されることがわかった。本研究により、高温超伝導における様々な輸送係数(ホール係数、磁気抵抗、熱起電力及びネルンスト係数)の複雑で特徴的な振舞いが、反強磁+超伝導揺らぎの理論に基づき統一的に理解できることが明らかになり、特に擬ギャップ領域において強力な超伝導揺らぎが発達していることが結論された。
    2.強相関電子系における熱・電気的輸送係数の一般理論:強相関電子系における熱流と電流が絡んだ輸送現象の研究の為には、電子相関に関する詳細な考察が必要である。Littingerの線型応答理論('64)によると熱起電力は電流と熱流の相関関数より与えられるが、熱流のオペレーターは相互作用項に由来する2体項を含むため多体電子系では一般に複雑であり、バーテックス補正の理論的解析は過去不十分であった。我々は局所的エネルギー保存則から導かれるワード恒等式に着目して,熱起電力やネルンスト係数に対する厳密かつ簡便な一般的表式を導出した。これらの表式に含まれるバーテックス補正(前方散乱項)Γ^Iを,ワード恒等式Γ^I=δΣ/δGをみたすよう計算することで,各種輸送係数に対する保存則を満たす近似(Baym-Kadanoffのconserving approximation)がはじめて可能となった。

  25. 高温超伝導関連物質の輸送現象における非フェルミ液体的挙動:ホール効果、磁気抵抗

    Grant number:11740191  1999

    奨励研究(A)

    紺谷 浩

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    Grant amount:\1200000 ( Direct Cost: \1200000 )

  26. Many-body Problems in Condensed Matter Physics

    Grant number:07044066  1995 - 1996

    Grant-in-Aid for international Scientific Research

    UEDA Kazuo

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    The international collaboration on the spin gap phase of the plaquette RVB state has started during the period of this project and has been evolved into the study on the critical behavior of the quantum phase transition between the Neel ordered phase and the plaquette RVB phase. By employing the quantum loop algorithm Monte Carlo simulations it is shown that the critical exponents agree with the classical O (3) exponents, which supports the mapping to the nonlinear sigma model.
    Another important problem studied in this project is the metal-insulator transition in two-dimension. By using quantum Monte Carlo simulations and the scaling theory, it is concluded that the hyperscaling hypothesis is valid in this case and the dynamical exponent is z=4.
    Concerning the heavy Fermions, the one-dimensional Kondo lattice model was investigated by using the density matrix renormalization group. In the paramagnetic metallic phase, spin and charge Friedel oscillations were observed for the first time. From the period of oscillations it is concluded that the Fermi surface is large in the sense that the Fermi momentum is determined by the sum of densities of conduction electrons and the localized spins.
    For the ab-initio calculations of electronic states, the constant pressure molecular dynamics method was developed. This method enables us to determine the transition states of structural transformations in graphite, silicides, BC_2N and others.

  27. Devil's Staircase in Semimetals

    Grant number:07804020  1995 - 1996

    UEDA Kazuo

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    Authorship:Coinvestigator(s) 

    Among the magnetic materials known so far, CeSb has the most complex phase diagram as a function of temperature and magnetic field. The complex magnetic phase diagram is know as the devil's staircase. Generally, the series of CeX (X=P,As, Bi, Sb) have complex magnetic phase diagrams in different degree, which suggeststhat there is a common mechanism for the devil's staircase observed in CeX.A characteristic feature of CeX is smallness of carriers. The carriers of CeX consist of holes at the GAMMA point and electrons at the X points. Under this situation, a new type of scattering processes from holes to electrons and vice versa accompanied by spin exchange with f-spins. This process may be calledoff-diagonal exchange in contrast to the usual exchanges where the scattering are within a band. The momentum transfer associated with his off-diagonal exchange corresponds to the antiferromagnetic wave vector, favoring antiferromagnetic RKKY interaction among the f spins. On the other hand, the ordinary exchanges favor ferromagnetic coupling in the low carrier limit. In this project, we have shown that the frustration between the RKKY interactions originated from these two types of exchange mechanisms is the basic mechanism for the devil's staircase in CeX by using a simple one-dimensional model.
    Since the origin of the RKKY interaction can be traced back to the Friedel oscillations, we have proceeded to study the spin and charge Friedel oscillations in the Kondo lattice model. By using the
    density matrix renormalization group method, we have observed spin and charge Friedel oscillations. From the period it is concluded that the Fermi volume is large in the sense that the Fermi wavevector isdetermined by the sum of densities of conduction electrons and localized spins.

  28. 準二次元電子系の輸送現象

    Grant number:07237208  1995

    上田 和夫

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    Authorship:Coinvestigator(s) 

    高温超伝導の特徴は、2次元的なCuO_2面にキャリアーをドープして超伝導が実現している点にある。特にアンダード-ピングの領域では、NMRの緩和率などにスピン励起が抑制された擬ギャップ的な振舞いが観測されて、高温超伝導機構を理解する一つの鍵と考えられている。今年度始まった新たなテーマとして2次元モット絶縁体で、スピンギャップが観測されているCaV_4O_9に注目し、その機構について理論的考察を行なった。このシステムは2次元的で、スピン1/2ハイゼンベルグモデルが良い模型になっていると考えられるが、その特徴は、正方格子から1/5のスピンを規則的に抜いたことにある。この時4このスピンからなるプラケットが2次元的につながった構造を持っている。我々は、この構造がスピンギャップ形成に有理であることを指摘した。しかし、最近接相互作用のみの時にはまだ反強磁性秩序が残っていることを明らかにし、フラストレーションを引き起こす次近接相互作用の重要性を示した。
    モット絶縁体をドープした時の準二次元的伝導を考察するには、いずれにしても三次元性を考慮する必要がある。伝導の問題と、一体グリーン関数の自己エネルギーは密接な関係にあり、我々は面内と面間のトランスファーが著しくことなる系を考え、その自己エネルギーをスピンの揺らぎについてone-loopの近似で計算することを計画している。今年度は、準備として完全な三次元の係を考え自己エネルギーの計算を完了し、さらにそれを用いて三次元における反強磁性スピン揺らぎの機構による超伝導を考察した。その結果、二次元より転移温度が低い傾向はあるものの、スピン揺らぎに対して適当なパラメータを仮定すれば、やはりd-波超伝導が可能となることが明らかになった。これは重い電子系の超伝導に関連して興味深い結果と考えられる。

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Teaching Experience (On-campus) 6

  1. statistical physics II

    2018

  2. quantum mechanics IV

    2018

  3. statistical physics III

    2018

  4. 物理学基礎演習I

    2011

  5. 統計物理学I

    2011

  6. 物性物理学1

    2011

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