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Optimization variational Monte Carlo studies of pairing symmetry in cobaltate superconductors

Research Project

Project/Area Number 16540306
Research Category

Grant-in-Aid for Scientific Research (C)

Allocation TypeSingle-year Grants
Section一般
Research Field Condensed matter physics II
Research InstitutionTohoku University

Principal Investigator

YOKOYAMA Hisatoshi  Tohoku University, Graduate School of Science, Research Associate, 大学院理学研究科, 助手 (60212304)

Co-Investigator(Kenkyū-buntansha) OGATA Masao  Tohoku University, University of Tokyo, Graduate School of Science, Associate Professor, 大学院理学系研究科, 助教授 (60185501)
Project Period (FY) 2004 – 2006
Project Status Completed (Fiscal Year 2006)
Budget Amount *help
¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2006: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2005: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2004: ¥1,500,000 (Direct Cost: ¥1,500,000)
Keywordscobaltate / pairing symmetry / triangular lattice / variational Monte Carlo method / frustration / Mott transition / non-monotonic d-wave gap / doublon-holon binding / ダブロン-ホロン束縛 / コバルト水和物 / 有機κ-ET塩 / ペアリング対称性 / 超伝導 / t-Jモデル / 相分離 / 長岡強磁性
Research Abstract

In the last fiscal year, using an optimization variational Monte Carlo (VMC) method, we studied ground-state and low-energy properties of single-band Hubbard models and its strongly correlated version t-J models on anisotropic triangular lattices, which is considered to be plausible models of the newly-found superconducting cobaltates.
As a continuation of these studies for the single-band models, in this year, we mainly studied ground-state properties of a two-band Hubbard model, in particular, a stable condition of superconductivity and its pairing symmetry, because it is probable that the degeneracy of d orbitals are important in the cobaltate. Assuming a simple one-electron structure which roughly fits the band structure near Fermi surface of the cobaltate, we performed VMC calculations with changing the strength of electron correlation and electron density. As a result, we found that superconducting states with s-, d-and p-waves and some mixed waves like a d+id-wave become stable only when an isolated pocket-type Fermi surface overlaps with van-Hove-singularity points near half filling. Among these symmetries, the d+id is the most stable. This stabilization of the superconducting states originates in the gain in interaction energy, which is induced by the enhancement of antiferromagnetic (AF) correlation, as in the cuprate superconductors.
As another topic, we also studied Mott transitions and existence of superconductivity near the transition in a Hubbard model on frustrated square lattices with diagonal hoppings. The main result we obtained is that, for doped cases, the sign of diagonal hopping is crucial; for realistic correlation strength,.a metallic AF order appears for the positive sign (corresponding to electron-doped cases), whereas AF states lose intrinsic stability and phase separate to the regions of an AF state with the half-filled density and of a d-wave superconducting state with a high doping ratio.

Report

(4 results)
  • 2006 Annual Research Report   Final Research Report Summary
  • 2005 Annual Research Report
  • 2004 Annual Research Report
  • Research Products

    (20 results)

All 2007 2006 2005 2004

All Journal Article (20 results)

  • [Journal Article] Superconducting states in a two-orbital Hubbard model on a triangular lattices2007

    • Author(s)
      K.Kobayashi, H.Yokoyama
    • Journal Title

      Journal of Magnetism and Magnetic Materials 310

      Pages: 651-653

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2006 Annual Research Report 2006 Final Research Report Summary
  • [Journal Article] Superconductivity and a Mott transition in a Hubbard Model on an anisotropic triangular lattice model2006

    • Author(s)
      T.Watanabe, et al.
    • Journal Title

      Journal of Physical Society of Japan 75

      Pages: 74707-74707

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2006 Final Research Report Summary
  • [Journal Article] Mott Transitions and Superconductivity in Half-Filled-Band Hubbard Model on Square Lattice with Geometric Frustration2006

    • Author(s)
      H.Yokoyama, et al.
    • Journal Title

      Journal of Physical Society of Japan 75

      Pages: 114706-114706

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2006 Annual Research Report 2006 Final Research Report Summary
  • [Journal Article] Effect of next-nearest-neighbor transfer on superconductivity and antiferromagnetism in two-dimensional t-J model2006

    • Author(s)
      T.Watanabe, et al.
    • Journal Title

      Journal of Physics and Chemistry of Solids 67

      Pages: 112-114

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2006 Annual Research Report 2006 Final Research Report Summary
  • [Journal Article] Variational ground state of a two-orbital Hubbard model2006

    • Author(s)
      K.Kobayashi, H.Yokoyama
    • Journal Title

      Journal of Physics and Chemistry of Solids 67

      Pages: 1384-1387

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2006 Annual Research Report 2006 Final Research Report Summary
  • [Journal Article] Stability of the superconducting state in the two-band Hubbard model on a triangular lattice2006

    • Author(s)
      K.Kobayashi, H.Yokoyama
    • Journal Title

      Physica C 445-448

      Pages: 162-165

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2006 Final Research Report Summary
  • [Journal Article] Superconductivity and a Mott transition in a Hubbard Model on an anisotropic triangular lattice model2006

    • Author(s)
      T.Watanabe, et al.
    • Journal Title

      J. Phys. Soc. Jpn 75

      Pages: 74707-74707

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2006 Final Research Report Summary
  • [Journal Article] Mott Transitions and Superconductivity in Half-Filled-Band Hubbard Model on Square Lattice wi th Geometric Frustration2006

    • Author(s)
      H.Yokoyama, et al.
    • Journal Title

      J. Phys. Soc. Jpn. 75

      Pages: 114706-114706

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2006 Final Research Report Summary
  • [Journal Article] Effect of next-nearest-neighbor transfer on superconductivity and antiferromagnetism in two-dimensional t-Jmodel2006

    • Author(s)
      T.Watanabe, et al.
    • Journal Title

      Journal of Physics and Chemistry of Solids 67

      Pages: 112-114

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2006 Final Research Report Summary
  • [Journal Article] Superconductivity and a Mott transition in a Hubbard model on an anisotropic triangular lattice model2006

    • Author(s)
      T.Watanabe, et al.
    • Journal Title

      Journal of Physical Society of Japan 75

      Pages: 74707-74707

    • Related Report
      2006 Annual Research Report
  • [Journal Article] Stability of the superconducting state in the two-band Hubbard model on a triangular lattice,2006

    • Author(s)
      K Kobayashi, H. Yokoyama
    • Journal Title

      Physica C 445-448

      Pages: 162-165

    • Related Report
      2006 Annual Research Report
  • [Journal Article] Variational ground state of a two-orbital Hubbard model2005

    • Author(s)
      K.Kobayashi, H.Yokoyama
    • Journal Title

      Journal of Physics and Chemistry of Solids 66

      Pages: 1384-1387

    • Related Report
      2005 Annual Research Report
  • [Journal Article] Nonmonotonic dx2-y2-Wave Superconductivity in Electron-Doped Cuprates Viewed from the Strong-Cooupling Side2005

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

      Journal of the Physical Society of Japan 74

      Pages: 1942-1945

    • Related Report
      2005 Annual Research Report
  • [Journal Article] Variational Monte Carlo studies of a t-J model on an anisotropic triangular lattice2005

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

      Physica C 426-431

      Pages: 289-294

    • Related Report
      2005 Annual Research Report
  • [Journal Article] Pairing symmetry and ferromagnetism in the t-J model on a triangular lattice2005

    • Author(s)
      T.Watanabe et al.
    • Journal Title

      Physica C (印刷中)

    • Related Report
      2004 Annual Research Report
  • [Journal Article] Variational ground state of a two-orbital Hubbard model2005

    • Author(s)
      K.Kobayashi, H.Yokoyama
    • Journal Title

      Journal of Physics and Chemistry of Solids (印刷中)

    • Related Report
      2004 Annual Research Report
  • [Journal Article] Kinetic-Energy Pairing and Condensation Energy in Cuprates2005

    • Author(s)
      M.Ogata et al.
    • Journal Title

      Physica C (印刷中)

    • Related Report
      2004 Annual Research Report
  • [Journal Article] Stability of superconductivity and antiferromagnetism in two-Dimensional Hubbard model with diagonal transfer2005

    • Author(s)
      H.Yokoyama et al.
    • Journal Title

      Physica C (印刷中)

    • 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 et al.
    • Journal Title

      Journal of Physical Society of Japan 73

      Pages: 1119-1122

    • NAID

      110001954819

    • Related Report
      2004 Annual Research Report
  • [Journal Article] Variational Monte Carlo Studies of a t-J model on an Anisotropic triangular lattice2004

    • Author(s)
      T.Watanabe et al.
    • Journal Title

      Journal of Physical Society of Japan 73

      Pages: 3404-3412

    • Related Report
      2004 Annual Research Report

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Published: 2004-04-01   Modified: 2020-05-15  

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