石墨烯体系中一维拓扑受限电子态输运性质的研究

In graphene, due to its special honeycomb-lattice structure, there are three binary degrees of freedom: real spin, A/B sublattice pseudospin, and K/K' valley pseudospin. Through manipulating these degrees of freedom, various nontrivial bulk band gap can open at the Dirac points. A much more practical scheme is to apply a perpendicular electric field in bilayer graphene. The resulting bulk band gap can host a valley Hall effect. When the electric field varies spatially, a zero mode can appear along the lines with zero electric field (the corresponding valley topologies are opposite in the opposite regimes). Our previous research found that this zero-mode shows zero band resistance and a geometry-dependent counterintuitive current partition law. In this project, we mainly focus on: (1) the theory of the zero bend resistance and counterintuitive current partition, and finding the current partition law for the general topological intersections; (2) the external control of the current partition at topological intersections, and extending these studies to the fields of quantum anomalous Hall effect and two-dimensional topological insulators; and (3) explaining why the experimentalists cannot observe the topological zero-line mode and providing a realizable setup.

石墨烯独特的蜂窝状六角晶格结构决定了其特有的多种双重自由度：电子自旋、A/B子晶格赝自旋、K/K'谷赝自旋、以及多层石墨烯的上/下层组成的赝自旋。通过外部操控这些自由度，可以在狄拉克点打开各种非平庸的体能隙。其中较易实现的实验方案便是在AB型的双层石墨烯上外加一个垂直的电场。由此打开的非平庸的体能隙可以实现量子谷霍尔效应。当电场随空间变化时，在零电场处（两边具有相反的谷拓扑性质）会形成一种零模电子态。我们前期的计算发现，该态呈现零弯曲阻力特性，以及在拓扑交叉处存在与几何构型相关的反常电流分配现象。在本项目中，我们的研究将主要集中在以下几点：（1）理论解释零弯曲阻力和反常电流分配的根本原因，并揭示与几何构型相关的严格电流分配规律；（2）利用外部手段调控拓扑交叉处的电流分配，并将研究对象拓展到量子反常/自旋霍尔体系；（3）探讨实验上目前无法观测到该拓扑态的原因并提供一个实验可行性方案。

本课题围绕基于石墨烯的拓扑受限一维电子态的器件设计和电学输运特性进行了系列深入研究。从拓扑受限电子态的实验难点出发进行了分析，并给出了可行性实验原形的设计方案；对拓扑缺陷引起的受限电子态以及弯曲石墨烯等特殊构型进行了理论预测；对拓扑受限交叉点处的电流分配特性进行了探究，发现了反常的电流分配规律；联合实验团队首次在双层石墨烯体系中观测到拓扑受限电子态。在本基金的支持下，围绕相关研究主题共发表21篇文章，其中1篇Nature，1篇Nature Nanotechnology，2篇PRL，1篇NatureCommunications, 10篇PRB，1篇Reports on Progress in Physics，2篇Frontiers of Physics。该系列研究将有助于将基于石墨烯的电控拓扑电子态应用于低耗散电子元器件的设计和应用领域。