拓扑半金属等有序态及其新奇物性的研究

Recently, with the development of TI, many new topological states are predicted and identified, such as quantized anomalous Hall effect (QAHE), Dirac/Weyl semimetal, magnetic monopole and Majorana fermions. All of them can be classified as the non-trivial topological phenomena and realized in topological materials. As new quantum matter states, many topological phenomena have attracted tremendous interests not only because of their fascinating electronic properties, such as 3D linear dispersion and large quantum linear magnetoresistance, but also the great valuable applications in future spintronic devices designing and fault-tolerant quantum computers. In this project, we will develop a new universal algorithm to calculate the topological order for both cases preserve and absent of time-reversal symmetry. Using this method, we intend to explore the interactions between topological order and other quantum ordered states, such as ferromagnetic state and superconducting. Then, based on the first-princeples calculations, using LDA+Gutzwiller and LDA+DMFT to deal well with the correlated system，we will search widely in transition metal compounds to find new magnetic topological materials and topological superconductors. Besides, combined with advanced ARPES, STM and other advanced experimental methods, we will give basic theoretical explanation for experimental datas of novel topological properties.

近年来，随着对拓扑绝缘体的深入研究，许多新奇的拓扑物性被预言和发现，如量子反常霍尔效应、拓扑半金属、磁单极和Majorana费米子等，它们共同够成了庞大的拓扑家族。作为一种全新的量子物态，拓扑材料因其丰富奇特的电子特性，如三维空间线性色散，大的量子线性磁阻等，以及在未来自旋电子器件和容错量子计算机中的潜在应用价值，在世界范围内取得了快速发展，并成为凝聚态物理中的一个热点领域。本研究项目拟发展一套计算拓扑数的普适性方法，从不需要人为参数的第一性原理计算出发，结合Gutzwiller和DMFT方法可以用来处理较大的真实系统或能进行电荷密度或晶体结构的自洽优化，从而更精确地处理各种材料中的量子有序态，广泛搜寻过渡金属化合物，探寻和发掘可能的拓扑新材料，为材料合成和实验研究提供理论指导和依据，同时结合先进的ARPES，STM等先进实验手段，对探测到新奇拓扑物性给出基本的理论解释。

继拓扑绝缘体之后，拓扑半金属由于其丰富而独特的量子输运行为而受到广泛关注。本人结合第一性原理计算方法，发展计算拓扑不变量的自主程序包，实现了拓扑材料的自动搜索。先后提出和预言了一些新奇的拓扑态和拓扑材料，比如第二类外尔半金属材料WTe2/MoTe2，磁性外尔半金属材料ZrCo2Sn，沙漏费米子材料KHgSb，以及具有拓扑性的超导材料FeSe(Te)和TaSe3等。同时与各个实验小组紧密合作, 进行了ARPES和STM研究，观测结果与理论计算符合良好。拓扑半金属的手征反常、负磁阻等量子输运行为将来有望应用于自旋电子学。