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Search for novel low-energy states in strongly correlated electron systems

Research Project

Project/Area Number 15540333
Research Category

Grant-in-Aid for Scientific Research (C)

Allocation TypeSingle-year Grants
Section一般
Research Field Condensed matter physics II
Research InstitutionUniversity of Tokyo

Principal Investigator

OGATA Masao  University of Tokyo, Department of Physics, Associate professor, 大学院・理学系研究科, 助教授 (60185501)

Co-Investigator(Kenkyū-buntansha) YOKOYAMA Hisatoshi  Tohoku University, Department of Physics, Research Associate, 大学院・理学研究科, 助手 (60212304)
Project Period (FY) 2003 – 2005
Project Status Completed (Fiscal Year 2005)
Budget Amount *help
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2005: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2004: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2003: ¥1,500,000 (Direct Cost: ¥1,500,000)
Keywordshigh-temperature superconductivity / variational Monte Carlo / high-temperature expansion / t-J model / optical sum rule / 時間反転対称性を破る超伝導 / Gutzwiller近似 / 凝集エネルギー / ハバードモデル / グッツウィラー近似
Research Abstract

In this study we planned to study novel low-energy states in strongly correlated electron systems using variational Monte Carlo method and analytical methods. In particular, we take account of the effects of strong correlation which cannot be treated in the mean-field theories and perturbative approaches.
We studied the mechanism of high-temperature superconductivity from a viewpoint of condensation energy. We evaluate the ground state energy by variational Monte Carlo method and study the condensation energy by comparing the energies of superconducting state and normal state. As a result, we conclude that the superconductivity is realized by gaining the kinetic energy in the strong correlation regime, which is opposite to the conventional BCS theory. In contrast, in the weak correlation regime, the system behaves similarly to the BCS theory.
As another method, we study the microscopic mechanism of the energy gain below Tc in fluctuation-exchange approximation, and obtain similar results. This is a characteristic phenomenon in high-temperature superconductors where the superconducting gap is very large and is due to the change of the renormalization parameters of quasiparticles by the gap. This result also explains the breakdown of the optical sum rule observed experimentally.
About the t-J model which is a typical model for strongly correlated electron systems, we study the superconducting correlation functions using high-temperature expansion method which is alternative to the variational Monte Carlo. In this method, the extrapolation to low temperatures is the most difficult part, but we carry out higher order calculations and succeed to evaluate physical quantities in low temperatures by combining a new extrapolation scheme. As a result, we show that the d-wave superconductivity correlation develops in the parameter space corresponding to the actual materials. This supports the results obtained in the variational Monte Carlo method.

Report

(4 results)
  • 2005 Annual Research Report   Final Research Report Summary
  • 2004 Annual Research Report
  • 2003 Annual Research Report
  • Research Products

    (13 results)

All 2005 2004 Other

All Journal Article (12 results) Publications (1 results)

  • [Journal Article] Development of Superconducting Correlation at Low Temperatures in the Two-dimensional t-J Model2005

    • Author(s)
      T.Koretsune, M.Ogata
    • Journal Title

      J. Phys. Soc. Japan 74

      Pages: 1390-1393

    • NAID

      110001979542

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2005 Final Research Report Summary
  • [Journal Article] Pairing correlation functions in the triangular t-J model : d-wave and f-wave superconductivity2005

    • Author(s)
      T.Koretsune, M.Ogata
    • Journal Title

      Phys. Rev. B 72

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2005 Final Research Report Summary
  • [Journal Article] Kinetic Energy, Condensation Energy, Optical Sum Rule and Pairing Mechanism in High-T_c Cuprates2005

    • Author(s)
      Y.Yanase, M.Ogata
    • Journal Title

      J. Phys. Soc. Japan 74

      Pages: 1534-1543

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2005 Final Research Report Summary
  • [Journal Article] Development of Superconducting Correlation at Low Temperatures in the Two-Dimensional t-J Model2005

    • Author(s)
      T.Koretsune, M.Ogata
    • Journal Title

      J.Phys.Soc.Japan 74

      Pages: 1390-1393

    • NAID

      110001979542

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2005 Final Research Report Summary
  • [Journal Article] Pairing correlation functions in the triangular t-J model : d-wave and f-wave superconductivity2005

    • Author(s)
      T.Koretsune, M.Ogata
    • Journal Title

      Phys.Rev.B 72

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2005 Annual Research Report 2005 Final Research Report Summary
  • [Journal Article] Kinetic Energy, Condensation Energy, Optical Sum Rule and Pairing Mechanism in High-Tc Cuprates2005

    • Author(s)
      Y.Yanase, M.Ogata
    • Journal Title

      J.Phys.Soc.Japan 74

      Pages: 1534-1543

    • NAID

      110001979568

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2005 Final Research Report Summary
  • [Journal Article] Development of Superconducting Correlation at Low Temperatures in the Two-dimensional t-J Model2005

    • Author(s)
      T.Koretsune, M.Ogata
    • Journal Title

      J.Phys.Soc.Japan 74

      Pages: 1390-1393

    • NAID

      110001979542

    • Related Report
      2005 Annual Research Report
  • [Journal Article] Kinetic Energy, Condensation Energy, Optical Sum Rule and Pairing Mechanisms in High-T_c Cuprates2005

    • Author(s)
      Y.Yanase, M.Ogata
    • Journal Title

      J.Phys.Soc.Japan 74

      Pages: 1534-1543

    • Related Report
      2005 Annual Research Report
  • [Journal Article] Crossover of Superconducting Properties and Kinetic-Energy Gain in Two-Dimensional Hubbard Model2004

    • Author(s)
      H.Yokoyama, Y.Tanaka, M.Ogata, H.Tsuchiura
    • Journal Title

      J. Phys. Soc. Japan 73

      Pages: 1119-1122

    • NAID

      110001954819

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2005 Final Research Report Summary
  • [Journal Article] Crossover of Superconducting Properties, Kinetic-Energy Gain in Two-Dimensional Hubbard Model2004

    • Author(s)
      H.Yokoyama, Y.Tanaka, M.Ogata, H.Tsuchiura
    • Journal Title

      J.Phys.Soc.Japan 73

      Pages: 1119-1122

    • NAID

      110001954819

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2005 Final Research Report Summary
  • [Journal Article] Variational Monte Carlo Studies of Pairing Symmetry for the t-J Model on a Triangular Lattice2004

    • Author(s)
      T.Watanabe, H.Yokoyama, Y.Tanaka, J.Inoue, M.Ogata
    • Journal Title

      J.Phys.Soc.Japan 73

      Pages: 3404-3412

    • NAID

      110001979312

    • Related Report
      2004 Annual Research Report
  • [Journal Article] Crossover of Superconducting Properties and Kinetic-Energy Gain in Two-Dimensional Hubbard Model2004

    • Author(s)
      H.Yokoyama, Y.Tanaka, M.Ogata, H.Tsuchiura
    • Journal Title

      J.Phys.Soc.Japan 73

      Pages: 1119-1122

    • NAID

      110001954819

    • Related Report
      2004 Annual Research Report
  • [Publications] M.Ogata: "Superconducting states in Frustrating t-J model : A model connecting high-Tc cuprates, organic conductors and Nax Co O2"J.Phys.Soc.Japan. 72. 1839-1842 (2003)

    • Related Report
      2003 Annual Research Report

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Published: 2003-04-01   Modified: 2020-05-15  

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