拓扑绝缘体异质结中界面电子结构调控的研究

Topological insulator is one of the most important materials for fabricating nanoelectronic and spintronic devices. While being applied to devices, topological insulators will inevitably form heterojunctions with other materials. However, the electronic structures and physical properties of topological insulator heterojunctions have not been clearly revealed yet, which will restrict the design, fabrication and application of topological insulator devices. To clarify these issues, we will study the interfacial electronic structures and physical properties of heterojunctions composed of topological insulators (bismuth selenide, bismuth telluride and antimony telluride ) and other three classes of electronic functional materials. First, we will study the topological insulators/graphene heterojunction. We will investigate the modulation of Dirac fermions of the interface by external electric field, alkali metal, magnetic impurity and crystal defects. Second, we will study the topological insulators/metal electrodes heterojunctions. We will calculate the contact barrier, effective mass and mobility of topological surface state to find alternative Ohmic contacts. Finally, we will study the topological insulators/magnetic materials heterojunctions. We will explore the modulation of energy-momentum dispersion and spin-momentum locked character of topological surface state. The research of this project will deepen our understanding of the physical properties of topological insulators and provide theoretical basis and guidance for the application of topological insulators in electronic and spintronic devices.

拓扑绝缘体是制备新一代低功耗纳米电子和自旋电子器件的重要材料之一。在拓扑绝缘体器件的应用中，将不可避免地与其他材料形成异质结，但其异质结的电子结构及物性尚未被完全揭示，这将限制对拓扑绝缘体器件的设计、制备及应用。针对上述问题，本项目用第一性原理计算方法研究拓扑绝缘体（硒化铋、碲化铋、碲化锑）与三种电子功能材料异质结的电子结构及物性。首先研究拓扑绝缘体/石墨烯异质结，计算外加电场、碱金属、磁性杂质及晶格缺陷对这两种材料的狄拉克费米子的影响和调控；其次研究拓扑绝缘体/金属电极异质结，计算电接触势垒，界面拓扑态的有效质量, 迁移率，为拓扑绝缘体寻找合适的欧姆电极；最后研究拓扑绝缘体/磁性材料异质结，探索铁磁及反铁磁材料对拓扑绝缘体拓扑态的能量-动量色散关系及自旋分辨特性的调控。本项目的研究结果将加深我们对拓扑绝缘体物理特性的认识，为拓扑绝缘体在电子学及自旋电子学领域的应用提供理论依据和参考方法。

本项目研究了拓扑绝缘体、石墨烯、黑磷、过渡金属二硫属化物这四类前沿二维电子材料及其异质结的物理性质。研究的具体内容包括界面电子结构、电学、磁学、光学性质。主要研究方法是第一性原理计算、紧束缚模型计算，及与相关领域实验研究人员的合作研究。在石墨烯/几类拓扑绝缘体异质结发现了通过外加电场、分子吸附、氮化硼插层等调控狄拉克费米子的有效途径，并且可以调控自旋轨道耦合作用。在黑磷-硒化钨异质结发现了可以调控的线性色散的狄拉克电子态，并且发现了新颖的磁学性质，异质结具有较强的磁晶各向异性能，可以达到28.2 meV，在磁存储领域具有较大的应用潜力。石墨烯-黑磷平面内异质的结界面电子结构可以被量子尺寸效应及电场调控。在强电场下，可以在界面处开发出狄拉克-费米子，狄拉克费米子的费米速度可以达到10^5m/s。研究了磁性原子在过渡态金属二硫属化物纳米带的掺杂的热力学行为和磁学性质，解释了相关实验的具体表征结果。研究了化学吸附的有机物分子对石墨烯的电学和磁学性质调控，单个有机物分子甚至可以在石墨烯中注入3.5个玻尔磁子。研究了从碳纳米线，到碳纳米环、六角蜂窝状的碳纳米团簇的热力学和动力学的生长机制，揭示了了二维石墨烯的生长原理。