二维材料中拓扑电声耦合对霍尔类型输运影响的研究

Recently two-dimensional materials, including graphene and transition metal dichalcogenides, have been a focus of studies due to their abundant physical properties. A main topic among transport studies is associated with topology-related Hall-like phenomena, such as thermal Hall effect, spin and valley Hall effect. Generally, two-dimensional materials share two different types of topological carriers: topological electrons associated with the electronic Hall effect and topological phonons associated with the thermal Hall effect. When considering the coupling between such electrons and phonons, i.e., topological electron-phonon coupling, systems may exhibit distinct transport features from non-topological materials. However, current studies of electron-phonon coupling on electronic transport mainly focus on the longitudinal direction, whereas its role in Hall-like transport has so far received relatively less attention. In this project, we consider the transverse Hall effect of electrons induced by topological electron-phonon interaction in two-dimensional materials. By theoretical analysis and numerical calculations, we will predict and explain new physical phenomena. Furthermore, in contrast to the graphene system, transition metal dichalcogenides like MoS2 exhibit an unusual spin-valley coupled band structure. We will explore the effect of spin-valley coupling on the electron-phonon interaction and electronic transport. The results will offer understandings for new physics, and guidelines for experimental probes.

二维材料包括石墨烯、过渡金属硫化物等，因具有极其丰富的物理性质已成为近年来的研究热点。其中一个主要方向是与拓扑相关的各种霍尔类型的输运效应，譬如热霍尔、自旋和能谷霍尔效应等。二维材料通常具备两套不同的拓扑输运载体：与电霍尔效应相关的电子拓扑性质以及与热霍尔相关的声子拓扑性质。当进一步考虑拓扑电子与声子之间的耦合，即拓扑电声耦合，系统可能表现出与非拓扑材料完全不同的输运性质。然而目前考虑二维材料电声耦合对电子输运的影响还局限于径向输运问题，对霍尔类型输运的研究较少。本项目主要研究二维材料中拓扑电声耦合对电子横向霍尔类型输运的影响，并通过理论分析和数值计算，预言和解释新的物理现象。同时我们还强调，不同于石墨烯系统，过渡金属硫化物包括二硫化钼等具有特殊的的自旋-能谷耦合特性，我们将进一步研究此特性在电声耦合以及输运方面带来的独特之处。研究结果将预言和解释新的物理效应，并为实验观测提供理论依据。

近年来，二维类石墨烯材料如单层过渡金属硫化物等，因其特有的能带几何拓扑特性吸引了广泛的研究兴趣。这种几何拓扑特性不仅会影响系统中的电子性质，还会影响声子性质，甚至产生新的形式的电声相互作用。这些新型的电声相互作用反过来也会影响电子与声子的物理特性，带来新的可观测的物理效应，进而推动电子学以及声电子学的发展。本项目在这一方面开展研究，完成了以下几个工作：.(一) 我们系统研究了二维六角晶格材料中不同形式电声耦合作用对电子能谷霍尔效应的影响;.(二) 我们研究了单层过渡金属硫化物中磁化导致的声子圆二色性效应；.(三) 我们探讨了二维狄拉克材料中非互异的声子圆二色性效应的物理起源以及可能的形成机制。. 本项目共发表研究论文2篇，其中Physical Review B (Rapid Communications) 1篇，Physical Review B (Letters) 1篇；另有一篇论文在审稿中。