Effects of phonon, orbital and disorder on the Mott transition

声子、轨道和无序对莫特跃迁的影响

基本信息

批准号：
14540334
负责人：
ONO Yoshiaki
金额：
$ 2.5万
依托单位：
Niigata University (2003-2004)Nagoya University (2002)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

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.

1.利用动力学平均场理论研究了轨道简并哈伯德模型中的莫特金属-绝缘体转变。洪特规则交换 J 的包含导致临界值 U_c 的大幅降低。结果表明，这种转变发生了质的变化，从 J=0 时的连续到任意有限 J 时的不连续。 2.采用数值对角化方法研究了一维多轨道 Hubbard 模型。由于洪德规则耦合和晶体场分裂之间的竞争，完全极化的铁磁性相对于部分极化的铁磁性变得不稳定。在部分极化铁磁性附近观察到超导相。3.利用四分之一填充时的现场和最近邻相互作用，研究了一维扩展哈伯德模型中金属-绝缘体转变附近的临界行为数值对角化和重正化群的组合方法。4.研究了半填充 Holstein-Hubbard 模型中的金属-绝缘体跃迁作为现场电子-电子相互作用 U 和电子-声子耦合 g.当 U 占主导地位时，过渡到莫特绝缘体；当 g 占主导地位时，过渡到局部双极状态。在前一种情况下，转变总是二阶的，而在后一种情况下，当U.5值较大时，转变变成一阶。利用动态平均场理论研究了周期性Anderson-Holstein模型。在强电子-声子耦合状态下，系统表现出异常的重费米子行为，伴随着大的晶格涨落和极端的声子软化。弱耦合状态下离子的简谐振动势转变为强耦合状态下的有效双阱势。