典型二维六角晶格材料中谷相关电子输运特性的理论研究

Valleytronics has attracted intensive research interests from both condensed matter physics and material science fields. It aims to control and manipulate the valley degree of freedom of electron to carry information, and construct high-efficiency, low-cost valleytronic devices. In addition to charge and spin, valley is the new degree of freedom of electron and first discovered in 2-dimensional (2D) honeycomb-lattice materials. Graphene and transition metal dichalcogenides (TMDs) are typical 2D honeycomb-lattice materials. Study on the valley-related transport properties of these materials is of both fundamental and applicable importance. In this project, we will theoretically investigate the valley-related electronic transport characteristics of typical 2D honeycomb-lattice materials: graphene and TMDs. The adopted methodology is non-equilibrium Green’s function combing first-principle calculation, tight-binding model, and k-p model, etc. Our investigation will focus on the following subjects: the electric generation of pure valley current and setup of quantum valley source; strain effect on the valley transport properties of monolayer TMDs; quantum valley Hall effect and its statistical behavior in the presence of disorder, etc. We hope that the outcome of these investigations would promote the comprehension on the valley-related transport properties of typical 2D honeycomb-lattice materials, and provide certain theoretical reference for the design of valleytronic devices.

谷电子学是当前凝聚态物理和材料物理领域的研究热点之一，其目标是调控电子的谷自由度来传递信息，并构建高效率、低能耗的谷电子学器件。谷是材料中除电荷及自旋外新的可操控自由度，最早发现于二维六角晶格材料。石墨烯和过渡金属二硫化物是典型的二维六角晶格材料，对其谷输运特性的研究在谷电子学的基础理论和实际应用方面均有重要意义。本项目拟采用非平衡格林函数方法，结合第一性原理计算、紧束缚模型及低能有效模型等，对典型二维六角晶格材料石墨烯和过渡金属二硫化物的谷相关电子输运特性进行理论和数值研究。主要研究内容包括：纯谷流的电学产生和量子谷源的架构；应力对单层过渡金属二硫化物谷输运特性的影响；量子谷霍尔效应及其在无序下的统计行为描述等。这些研究将有助于提升对典型二维六角晶格材料谷相关输运特性的理解，为谷电子学器件设计提供理论参考，从而推动谷电子学的发展。

在特定的晶体材料中，电子除电荷和自旋自由度以外，还可能具有能谷自由度。谷电子学材料的研究是当前凝聚态物理的重点领域之一。在本研究项目中，我们利用非平衡格林函数方法，结合第一性原理和模型计算方法，详细探讨了典型二维六角晶格材料石墨烯和过渡金属二硫化物的谷电子学输运特性。项目的研究结果包括：（1）计算了石墨烯和碳纳米管超晶格的能带特性并提出了一种谷场效应管设计，可以通过门电压调控谷极化率；（2）研究了锯齿形石墨烯带的谷热电输运特性并讨论了退相干效应和随机硼、氮掺杂的影响；（3）利用绝热参数泵浦在石墨烯带中产生谷极化电流并分析了空间对称性的影响；（4）在双层二硫化钼系统中利用电学手段调控光致电流的谷极化率；（5）讨论了电磁波调控对单层过渡金属二硫化物中能谷激子的几何相位的影响；（6）利用交换场和Rashba自旋轨道耦合效应在单层二硫化钼中泵浦产生稳定的谷-自旋极化电流。这些研究结果丰富了对石墨烯和过渡金属二硫化物谷电子学输运特性的理解，并对潜在的谷电子学应用提供了理论依据。在项目执行期间，项目组共发表SCI论文15篇，包括3篇Physical Review B，2篇Carbon，2篇New Journal of Physics.