单层过渡金属硫化物中拓扑激子和能谷电子学相关理论研究

The emergent topologically nontrivial quantum states in the 2D materials are currently a frontier research field in solid state physics. As novel 2D semiconductor materials, the group VI transition metal dichalcogenides(TMDCs) not only have great potential applications in the field of valleytronics, but also provide the unprecedented platform to investigate the topological nontrivial quantum state in 2D materials. In this project we shall introduce the topological exciton in monolayer TMDC, which is considered as the consequence of the time-reversal symmetry breaking together with spin-orbital coupling. Such novel edge states will simultaneously influence the system transportation and fluorescence properties. Firstly, by utilizing the exciton spin-orbit coupling which is inherited from the electron-hole exchange interaction and introducing a position dependent magnetic field as the domain wall to break time reversal symmetry，this project will systematically study the formation mechanism of the topological exciton and its influence to the system's quantum properties. Secondly, by adjusting the external controlling magnetic field and the effective magnetic field resulting from the substrate strain, the dependences of the topological exciton quantum properties on those parameters will be revealed. Thirdly, the interplay between the system transportation and fluorescence properties will be investigated based on the charged topological exciton generated by increasing the electric bias. In this project we focus on the formation and the control of the topological exciton in monolayer TMDC, proposes a formalism to realize reliable quantum control of the valley degree of freedom, and facilitates the development of the quantum devices based on semiconductor optics and valleytronics.

在二维材料中实现拓扑非平庸的量子态是固态物理的前沿研究方向。作为新型的二维半导体材料，单层过渡金属硫化物不仅在能谷电子学方面有着巨大的应用前景，而且是用来研究拓扑非平庸量子态的良好平台。本项目将提出在单层过渡金属硫化物中破坏时间反演对称性后显示出拓扑非平庸性的是激子态，这是一种同时影响体系输运和荧光性质的新型边缘态。本项目将（1）利用激子继承自电子空穴交换相互作用的自旋轨道耦合，引入空间变化磁场畴壁破坏时间反演对称性，系统地研究拓扑激子的形成机制，探索其对体系量子性质的影响；（2）利用计算机模拟结合控制场的参数和衬底引入的等效磁场，揭示拓扑激子量子性质的变化规律；（3）通过加大偏压产生带电的拓扑激子，探求体系输运和荧光性质之间的相互影响。本项目着眼于以理论指导拓扑激子的产生和控制，提出利用它们的特性来实现能谷自由度的可控量子操纵，最终促进基于半导体光学和能谷电子学的量子器件的发展。

我们按照项目的研究计划，项目进展比较顺利，取得了一定的研究成果，已经发表了13篇SCI文章，还有两篇在投。我们主要研究了和单层过渡金属硫化物相关的各种异质结上的激子的光电学特性。我们研究了空间变化的磁场作用下单层二硫化钼中带手性的拓扑激子的形成机制、拓扑特性以及波函数分布。对于不同过渡金属硫化物的包括量子线、量子阱和量子点等各种类型的异质结，我们提出了基于紧束缚模型的哈密顿量，并在波恩奥本海默近似下进行数值求解，得到了体系激子的光电学特性。在量子力学基本问题方面，我们以约束在环上的耦合谐振子体系作为例子从理论上研究了在没有环境下的自发退相干的过程。