2004 Fiscal Year Final Research Report Summary
Effects of phonon, orbital and disorder on the Mott transition
| Project/Area Number |
14540334
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
固体物性Ⅱ(磁性・金属・低温)
|
|---|
| Research Institution | Niigata University (2003-2004)
Nagoya University (2002) |
|---|
Principal Investigator |
ONO Yoshiaki Niigata University, Faculty of Science, Professor, 理学部, 教授 (40221832)
|
|---|
| Project Period (FY) |
2002 – 2004
|
| Keywords | metal-insulator transition / Hubbard model / Mott insulator / electron-phonon interaction / bipolaron / heavy fermion / ferromagnetism / superconductivity |
|---|
| 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.
|
Research Products
(26 results)
