硅烯中自旋和能谷旋量的输运调控

As a novel two-dimensional Dirac electronic material, silicene, a single sheet of silicon atoms arranged in a low-buckled honeycomb lattice, has not only a traditional spin degree of freedom but also a nontraditional one akin to spin, namely valley spinor. Thus, similar to spin in spintronics, studying the transport and manipulation of spin/valley degree of freedom in silicene would become strongly desirable to understand the exotic properties silicene has and establish the theoretical basis for the construction of novel spin/valley-based logic devices. In this project, following the systematic analysis on the reported activities in silicene community, we will mainly focus on the spin/valley-polarized transport as well as its manipulation in silicene nanosystems in its bulk regime, a shaded scheme when comparing to that in its edge state regime. Based on the peculiar properties of silicene, we will firstly construct various silicene nanostructures like silicene junction, waveguide, quantum ring, and dot, and then investigate the intrinsic characteristics on the generation, transport, and relaxation of spin/valley- polarized current in the constructed structure by flexibly applying tight-binding model, nonequilibrium Green function, or model Hamiltonian method. Subsequently, we will further investigate the possible effect of realistic parameters like size, configuration, and disorder on the acquired transport characteristics. Finally, we will further impose various external strategies like electric, magnetic, and strain field to modulate the spin/valley-polarized transport properties in silicene nanostructures. To sum up, we hope, combining the results achieved in the edge-mode transport, to understand systematically the microscopic principle on the transport and manipulation of spin/valley-polarized beams in silicene, search feasible yet reliable strategies on the manipulation of spin and valley degree of freedom to guide the realistic logic device construction, identify the difference and relation between bulk mode transport and edge mode transport, and establish the solid scientific knowledge for the development of novel spin and valley-based logic devices in atomically silicene systems.

硅烯是由单层硅原子按翘曲蜂窝结构排列的新型二维狄拉克电子材料，具有自旋和能谷旋量，深入研究硅烯中自旋和能谷极化输运的基础理论及其调控机制可进一步加深对硅烯奇异物性的理解，确立相关非传统逻辑器件结构及其构建的理论基础。本研究在综合分析既有研究重边缘态物理而对体态物理认识不足的基础上，结合硅烯所呈现的新奇物性，通过构建硅烯结、波导、量子环、量子点等多尺度、不同位型的量子结构，灵活运用紧束缚方法、非平衡格林函数方法和模型哈密顿量方法等研究手段，系统剖析结构中体态自旋(能谷)极化产生、输运和弛豫的內禀特性及其在尺度、位型、无序等內禀参量调控和电、磁、应力等外部激励下的响应规律，阐明硅烯中自旋和能谷极化输运调控的微观机制，总结符合相关逻辑器件构筑实际的自旋(能谷)极化输运调控的可行可靠策略，细致甄别体模输运与边缘模输运之间的差异，为发展硅烯基非传统自旋(能谷)电子器件确立系统化的科学依据。

本项目以硅烯材料所具有的门电场可控的局域能隙、强的自旋-轨道耦合、自旋-能谷互锁等奇异物性为基础，运用模型哈密顿量方法研究硅烯结、硅烯点、硅烯环等介观结构中狄拉克电子的输运特性。项目组在动态结合硅烯研究领域的新进展的基础上，重点围绕硅烯结、硅烯量子环、硅烯量子点、硅烯波导等典型结构中能谷和自旋旋量态的输运调控开展了研究工作，建立了门控硅烯结构中狄拉克电子遂穿通过门垒的驻留时间与相位延迟时间之间的普适联系；发展了有效处理复合单/双层硅烯异质结结构中电输运特性的转移矩阵方法；系统研究了门控硅烯结构中驻留时间、Goos-Hänchen位移、散粒噪声等物理参量的表观行为及其在外场调制下的响应规律，为实验上标识和实现硅烯结构中旋量简并态的极化输运确立了有益的理论准则；系统研究了硅烯量子点和量子环中(准)束缚模态的分布特征及其在外场调控下的响应行为，为相关量子电子器件的构筑确立了物理基础；系统研究了不同束缚位型下硅烯波导结构模式分布，总结了不同外场调制对结构中波导模式的影响规律。总体而言，项目组以项目研究计划为主要参考，重点研究了硅烯结、点、环中狄拉克旋量态的输运调控特性，获得了一些具有实验指导意义的理论研究成果，基本实现项目预期研究目标，对硅烯结构中自旋和能谷旋量态的输运特性做了较为系统的回答。