Electron Correlation Effects in Frustrated Itinerant Electron Systems

在这个项目中，我们研究了强关联电子系统中的各种有趣的现象，这些系统在自旋和轨道自由度的影响下受到几何受挫。我们还致力于全面了解凝聚态物理的基本问题，即“电子关联和量子涨落”。为了从理论上处理这些具有大量子涨落的系统，我们需要使用平均场理论以外的复杂方法。一般来说，很难处理这样的问题，包括强电子关联和几何受挫。我们使用了一种强大的方法，即所谓的动态团簇近似，它使我们能够系统地研究受挫电子系统。此外，当我们从绝缘侧处理问题时，我们利用了计算机辅助的强耦合团簇展开，而在金属区域，我们使用了变分的蒙特卡尔…我们系统地研究了自旋、电荷和轨道自由度相互作用所产生的有趣现象。特别是，我们重点研究了量子相变和相关的临界现象。用这种方法，我们从微观的角度从理论上研究了强关联电子系统的动力学。我们着重研究了以下六个问题：1.受挫Mott绝缘体中的空穴效应；2.自旋-冰系统中的受挫效应；3.受挫导致的自发降维；4.近藤效应与RKKY相互作用之间的竞争；5.自旋和轨道自由度之间的竞争和相互作用；6.Kagome和棋盘格子上的相关电子系统。上述结果已在几个国际期刊上发表(30篇原始论文)。此外，我们还在国际会议和研讨会上报告了结果(12次应邀演讲)。虽然研究已经比较系统，但仍然存在与实验的定量对比，这将在以后的工作中加以考虑。较少

In this project, we have studied a variety of interesting phenomena in strongly correlated electron systems, which are subject to geometrical frustration under the influence of spin and orbital degrees of freedom. We have also aimed at comprehensive understanding of the fundamental problem of condensed matter physics, i.e. "electron correlations and quantum fluctuations". In order to theoretically treat these systems with large quantum fluctuations, we need make use of sophisticated methods beyond mean-field theory. In general, it is difficult to deal with such problems including both strong electron correlations and geometrical frustration. We have used a powerful method, the so-called dynamical cluster approximation, which enables us to study frustrated electron systems systematically. Also, we have exploited the computer-aided strong-coupling cluster expansion when we approach the problem from the insulating side, while in the metallic region, we have used the variational Monte Carl … More o method, etc. We have systematically investigated the interesting phenomena originating from the interplay of spin, charge and orbital degrees of freedom. In particular, we have focused on quantum phase transitions and related critical phenomena. In this way, we have studied the dynamics of strongly correlated electron systems theoretically from the microscopic point of view. We have investigated the above problem with particular emphasis on the following six subjects.1.hole-doing effect into frustrated Mott insulator.2.frustration effects in spin-ice systems.3.spontaneous dimensional-reduction due to frustration4.competition between the Kondo effect and the RKKY interaction.5.competition and interplay between spin and orbital degrees of freedom.6.correlated electron systems on the Kagome and checker-board lattice.The above results have been published (30 original papers) in several international journals. Also, we have reported the results (12 invited talks) in the international conferences and symposia. Although the research has been performed systematically, there still remains the quantitative comparison with experiments, which will be considered in the future work. Less