无能隙准粒子态及受对称性保护拓扑能带所引起的反常热电输运性质

Since the discoveries of graphene, topological insulator, Dirac semimetal, and Weyl semimetal, the quasiparticle excitations with linear dispersion in the condensed matter physics have been under intense focus in the recent years. Among these the topological states in these topological materials has triggered a lot of interest in particular in emergent Dirac, Weyl, and Majorana fermions. The studies are not only quench our thirst on fundamental physics but also provide the possibility to manipulate them for technological applications. We will investigate the contributions arisen from these excitations to the thermoelectric transport phenomena of Weyl semimetals related to the chiral anomaly under the magnetic field based on the experimental evidences and the predications from the first principle calculations. The influences of the relaxations processes due to the short-range disorder and the long-range interaction on the transport properties will be analyzed. With the studies of the Andreev reflections at the interface of Weyl-semimetal/topological-superconductor, we discuss the effects of the chiral anomaly and the topological properties emerging in the zero-energy flat bands. The chiral anomaly effect related to the intra- and inter-node scattering rate will be investigated. Based on the analysis of the Majorana zero-mode with the band gap structures for systems with different topologies, the contributions from the topologically trivial and nontrivial states from the destructive or constructive addition of the Chern number contributions from the Majorana will be studied. The behaviors of intrinsic contributions to the thermal Hell conductivity from different topological states will be investigated. We also explore the possibility for designing novel electronic devices using the unconventional properties bestowed upon Weyl fermions by the topological stability of the Weyl nodes.

自从石墨烯，拓扑绝缘体，狄拉克半金属和外尔半金属的发现以来，凝聚态系统中具有线性色散关系的准粒子态备受关注，其中拓扑态触发许多与狄拉克，外尔，和马厩若纳费米子相关的有趣现象。对它们的研究不仅仅是出于对基础物理的兴趣，更为重要的是在应用方面利用电子相对论性质拓扑材料为实现和制备新型量子器件提供理论基础。结合实验和能带计算所预言的具有非平庸能带拓扑新材料，我们将对磁场下外尔半金属费米能级在外尔点附近变化的热电响应进行研究，就起源于短程无序和长程相互作用的弛豫对结果影响做相应的分析和讨论。结合外尔半金属和超导体界面的 Andreev反射的研 究，分析其手征反常效应和边缘态中平直能带的拓扑，讨论马厩若纳膜等新奇现象的物理起源，并讨论与不同外尔点间散射相关的手征反常效应。通过对拓扑不同系统的能隙结构导致的探索马厩若纳能带陈数所引起的破坏或建设性贡献导致的拓扑平庸和非平庸态，研究不同的拓扑态对热霍尔电导所产生的不同本征贡献行为。通过这些研究，期望探究外尔半金属系统中衍生的新物质相和讨论利用外尔费米载流子受保护的性质设计新电子器件的可行性。

在近年来结合量子材料中调控量子态的大背景下，我们开展了对狄拉克费米和外尔费米子等无能隙准粒子态的物理性质和对应凝聚体拓扑能带对电、热、光响应中表现做了分析研究。研究不仅能对凝聚态基础物理中准粒子激发的性质有所了解，同时对电子设备的研究打开一扇新的大门。. 针对外尔超导中可能的FFLO和BCS配对机制，研究中分析了BCS与FFLO配对机制相互作用产生混合机制的可能性。研究发现BCS+FFLO机制的双有效能隙结构，并讨论了能隙结构在外尔半金属与外尔超导界面Andreev反射现象探测中的印证。在BCS机制强时，在费米面上会出现环状节点，但是环状节点会随着FFLO机制的增强而消失。我们还研究了强磁场下外尔半金属与外尔超导界面在BCS和FFLO配对机制下的边缘态，分析了电导对费米能的依赖关系。利用弹道输运的Landauer-Buttiker公式计算了电导，证明了横向电导的拓扑属性。利用拓扑材料的性质实现电导1或者0态转换，我们提出设计拓扑场效应管的新思路。该场效应管是通过调控电子在拓扑边缘态之间的遂穿过程而不是拓扑相变来实现电导的0 或1 态，从而避开了调控拓扑相变的困难，实现电场调控的无拓扑相变拓扑场效应管。结合非厄米陈-绝缘体，对应于不同质量项与耗散项参数，对非厄米费米子系统的拓扑相进行了分类：狄拉克半金属，狄拉克半导体，非厄米狄拉克半导体，非厄米狄拉克半金属，和非厄米费米弧。导出推广的线性响应公式，讨论了非厄米效应对体系光电导的实部和虚部的影响。这些结果有望能够促进人们对非厄米体系输运性质的认识。基于自旋轨道耦合与铁磁作用的交互会衍生出有效的SU(2)电磁场，我们构建了SU(2)表述下的闭路和实时格林函数理论，研究了与SU(2) 外场相耦合的SU(2) 自旋轨道磁化。