关联电子系统奇异物性的数值计算模拟研究

As a new quantum state, topological insulator now is a very hot research topic in condensed matter physics. Most of the currently known or proposed topological insulators have small electronic correlation, thus are nonmagnetic compounds. Very recently, searching possible new topological quantum states in the materials with strong electronic correlation attract intensive research interesting. 4f and 5f materials have not only strong spin-orbital coupling but also large quite strong electron-electron interaction, thus to investigate these compounds is of both fundamental and technological importance. By using the local density approximation plus dynamical mean field theory (LDA+DMFT) as well as effective model, we will study the electronic structure and magnetic properties of 4f and 5f electronic systems. We will focus on Ce, Sm, Eu, Yb, U and Am, and study the effect of lattice structure and pressure. We will study the effect of electron-electron interaction and spin orbital coupling. We will also try to search possible new topological quantum state such as Axion insulator, Weyl semimetal, magnetic monopole etc.

拓扑绝缘体是最近几年发现的一类新的量子材料，是凝聚态物理的研究热点。现在已知的或者已经被预言的拓扑绝缘体基本上都是s/p电子体系，它们只有很弱的电子关联，所以基本都是有时间反演不变的非磁性材料。当前一大热点研究课题就是在电子关联较强的体系里面探寻可能的拓扑非平庸态。4f和5f电子体系都有着很强的自旋轨道耦合也有很大的电子关联效应。所以系统的对它们进行研究有重要的学术价值和巨大的应用前景。本项目拟用LDA+DMFT方法和有效模型分析相结合研究4f和5f电子体系。重点研究Ce、Sm、Eu、Yb等4f元素以及U、Am等5f元素的氧化物、硫族化合物的电子结构和磁性性质。研究晶体结构、压力对材料性质的影响。着重探讨电子关联和自旋轨道耦合共同作用对材料的独特影响。探寻可能的新拓扑量子态（如：有特别磁电响应的Axion绝缘体、Weyl半金属、可能的影像磁单极等）。

通过四年的努力，项目对以5d过渡金属材料体系为代表的强自旋轨道耦合电子关联体系物性研究上取得了进展。主要的工作为：（1）确定WTe2为第二类Weyl半金属；（2）理论预言压力能够使得WTe2表现拱形超导并被实验验证；（3）提出WTe2费米面自旋分布对其巨大磁电阻有重要贡献；（4）研究了压力对Weyl半金属TaAs家族、拓扑量子体系ZrTe5性质的影响；（5）预言了多个体系为拓扑半金属；（6）预言奇异电声子耦合导致p波超导体。共完成学术论文27篇，其中2篇Physical Review Letters；4 篇Nature Communications；5 篇Physical Review B；2 篇Scientific Reports。这27篇论文被SCI他人引用479次。所发表论文有4篇为ESI高被引论文。