| Project/Area Number |
14540334
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | Niigata University (2003-2004)
Nagoya University (2002) |
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Principal Investigator |
ONO Yoshiaki Niigata University, Faculty of Science, Professor, 理学部, 教授 (40221832)
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 2004: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2003: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2002: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Keywords | metal-insulator transition / Hubbard model / Mott insulator / electron-phonon interaction / bipolaron / heavy fermion / ferromagnetism / superconductivity / 充填スクッテルダイト化合物 / PrOs_4Pb_<12> / ラットリング / フォノン / 周期的アンダーソン模型 / 動的平均場理論 / 電子格子相互作用 / 近藤半導体 / スクッテルダイト / 厳密対角化法 / モット転移 / 電子相関 / フント則結合 / 軌道自由度 |
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| Research Abstract |
1.The Mott metal-insulator transition in the orbitally degenerate Hubbard model is studied by means of the dynamical mean-field theory. Inclusion of the Hund's rule exchange J results in a strong reduction of the critical value U_c. The transition turns out to change qualitatively from continuous for J=0 to discontinuous for any finite J.
2.The multi-orbital Hubbard model in one dimension is studied using the numerical diagonalization method. Due to the competition between Hund's rule coupling and crystal-field splitting, the fully polarized ferromagnetism becomes unstable against the partially polarized one. The superconducting phase is observed in the vicinity of the partially polarized ferromagnetism.
3.The critical behavior near the metal-insulator transition in the one-dimensional extended Hubbard model with the on-site and the nearest-neighbor interactions at quarter filling is studied using a combined method of the numerical diagonalization and the renormalization group.
4.The metal-insulator transitions in the half-filled Holstein-Hubbard model is investigated as a function of the on-site electron-electron interaction U and the electron-phonon coupling g. When U is dominant the transition is to a Mott-insulator ; when g dominates, the transition is to a localized bipolaronic state. In the former case, the transition is always found to be second order, while, in the latter case, it becomes first order for larger values of U.
5.The periodic Anderson-Holstein model is studied by using the dynamical mean-field theory. In the strong electron-phonon coupling regime, the system shows an anomalous heavy-fermion behavior which is accompanied by a large lattice fluctuation and an extreme phonon softening. A simple harmonic potential for ions in the weak coupling regime changes into an effective double-well potential in the strong coupling regime.
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