### 抄録

We preform a multi-orbital analysis on the novel superconductivity in Na_{x}CoO_{2}·yH_{2}O. We construct a three-orbital model which reproduces the band structure expected from the LDA calculation. The effective interaction leading to the pairing is estimated by means of the perturbation theory. It is shown that the spin triplet superconductivity is stabilized in the wide parameter region. This is basically owing to the ferromagnetic character of spin fluctuation. The p-wave and f-wave superconductivity are nearly degenerate. The former is realized when the Hund's rule coupling is large, and vice versa. In a small part of the parameter space, the d-wave superconductivity is also stabilized. We point out that the orbital degeneracy plays an essential role for these results. In particular, the momentum dependence of wave function of quasi-particles is quite important. The nearly degeneracy of p-wave and f-wave superconductivity is explained by analysing the microscopic character of each Fermi surface. We discuss the validity of some reduced models. While the single-orbital Hubbard model reproducing the Fermi surface is qualitatively inappropriate, we find an effective two-orbital model appropriate for studying the superconductivity. We investigate the vertex corrections higher than the third order on the basis of the two-orbital model. It is shown that the vertex correction induces the screening effect but does not affect qualitative results.

元の言語 | English |
---|---|

ページ（範囲） | 430-444 |

ページ数 | 15 |

ジャーナル | Journal of the Physical Society of Japan |

巻 | 74 |

発行部数 | 1 |

DOI | |

出版物ステータス | Published - 2005 1 |

外部発表 | Yes |

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### ASJC Scopus subject areas

- Physics and Astronomy(all)

### これを引用

*Journal of the Physical Society of Japan*,

*74*(1), 430-444. https://doi.org/10.1143/JPSJ.74.430

**Multi-orbital analysis on the superconductivity in NaxCoO 2·yH2O.** / Yanase, Youichi; Mochizuki, Masahito; Ogata, Masao.

研究成果: Article

*Journal of the Physical Society of Japan*, 巻. 74, 番号 1, pp. 430-444. https://doi.org/10.1143/JPSJ.74.430

}

TY - JOUR

T1 - Multi-orbital analysis on the superconductivity in NaxCoO 2·yH2O

AU - Yanase, Youichi

AU - Mochizuki, Masahito

AU - Ogata, Masao

PY - 2005/1

Y1 - 2005/1

N2 - We preform a multi-orbital analysis on the novel superconductivity in NaxCoO2·yH2O. We construct a three-orbital model which reproduces the band structure expected from the LDA calculation. The effective interaction leading to the pairing is estimated by means of the perturbation theory. It is shown that the spin triplet superconductivity is stabilized in the wide parameter region. This is basically owing to the ferromagnetic character of spin fluctuation. The p-wave and f-wave superconductivity are nearly degenerate. The former is realized when the Hund's rule coupling is large, and vice versa. In a small part of the parameter space, the d-wave superconductivity is also stabilized. We point out that the orbital degeneracy plays an essential role for these results. In particular, the momentum dependence of wave function of quasi-particles is quite important. The nearly degeneracy of p-wave and f-wave superconductivity is explained by analysing the microscopic character of each Fermi surface. We discuss the validity of some reduced models. While the single-orbital Hubbard model reproducing the Fermi surface is qualitatively inappropriate, we find an effective two-orbital model appropriate for studying the superconductivity. We investigate the vertex corrections higher than the third order on the basis of the two-orbital model. It is shown that the vertex correction induces the screening effect but does not affect qualitative results.

AB - We preform a multi-orbital analysis on the novel superconductivity in NaxCoO2·yH2O. We construct a three-orbital model which reproduces the band structure expected from the LDA calculation. The effective interaction leading to the pairing is estimated by means of the perturbation theory. It is shown that the spin triplet superconductivity is stabilized in the wide parameter region. This is basically owing to the ferromagnetic character of spin fluctuation. The p-wave and f-wave superconductivity are nearly degenerate. The former is realized when the Hund's rule coupling is large, and vice versa. In a small part of the parameter space, the d-wave superconductivity is also stabilized. We point out that the orbital degeneracy plays an essential role for these results. In particular, the momentum dependence of wave function of quasi-particles is quite important. The nearly degeneracy of p-wave and f-wave superconductivity is explained by analysing the microscopic character of each Fermi surface. We discuss the validity of some reduced models. While the single-orbital Hubbard model reproducing the Fermi surface is qualitatively inappropriate, we find an effective two-orbital model appropriate for studying the superconductivity. We investigate the vertex corrections higher than the third order on the basis of the two-orbital model. It is shown that the vertex correction induces the screening effect but does not affect qualitative results.

KW - Ferromagnetic spin fluctuation

KW - Multi-orbital analysis

KW - NaCoO·yHO

KW - Unconventional superconductivity

UR - http://www.scopus.com/inward/record.url?scp=18244387657&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=18244387657&partnerID=8YFLogxK

U2 - 10.1143/JPSJ.74.430

DO - 10.1143/JPSJ.74.430

M3 - Article

AN - SCOPUS:18244387657

VL - 74

SP - 430

EP - 444

JO - Journal of the Physical Society of Japan

JF - Journal of the Physical Society of Japan

SN - 0031-9015

IS - 1

ER -