外加电场对拓扑绝缘体薄膜中拓扑表面态和自旋劈裂的调控

Recently, it was found experimentally that there exists 2D electron gas in Bi2Se3-type TI and that the adsorption of alkali, heavy metal and magnetic atoms can lead to very large Rashba spin splitting. The adsorption of atoms and molecules is equivalent to application of an effective electric field to the TI surface. The external electric field is the most promising and popular approach to tune the Rashba spin orbit coupling strength in semiconductor heterostructures, which can be easily implemented in experiments. In this project, the variation of the surface states and the quantum well states of the Bi2Se3-type TI films with respect to the external electric field will be studied based on first-principles calculations. The TIs interfaced with different substrates(C, Si, GaAs), Bi and Pb films will be investigated, aiming to reveal the change of the interface states, quantum well states and the spin splitting under external electric field. We will also explore the relation between the contribution of the high order Rashba terms to the spin splitting and the applied electric field in Bi2Se3 type TIs. It is expected that new quantum phenomena and concepts will be discovered in our research, which will help to the design of new spintronic devices that can be effectively tuned.

最近，实验上发现了在Bi2Se3类拓扑绝缘体中存在二维电子气；在其表面吸附气体分子，碱金属原子，重金属原子，磁性原子等会产生显著的Rashba自旋劈裂。吸附原子，分子所起的作用类似于在拓扑绝缘体表面施加了外加电场。而外加电场是调控半导体异质结中二维电子气的自旋轨道耦合强度的一个最有希望和广泛采取的方式，在实验上也易于实现。本项目将基于第一性原理计算，研究在外加电场下,Bi2Se3类拓扑绝缘体薄膜的表面态，量子阱态的变化，自旋劈裂强度与电场大小之间的定量关系；研究在外加电场下，拓扑绝缘体与不同基底(石墨烯，Si，GaAs)，Bi，或Pb膜构成的系统中界面态，量子阱态的变化，自旋劈裂的变化；研究在Bi2Se3类拓扑绝缘体中的自旋劈裂中高阶Rashba项的贡献与外加电场之间的关系。相关研究可能会发现一些新量子现象和概念，并希望为从原理上设计一些功能易为调控的新型自旋电子器件提供物理基础。

在过去十年，实验上发现了在Bi2Se3类拓扑绝缘体中存在二维电子气；在其表面吸附气体分子，碱金属原子，重金属原子，磁性原子等会产生显著的Rashba自旋劈裂。吸附原子，分子所起的作用类似于在拓扑绝缘体表面施加了外加电场。而外加电场是调控半导体异质结中二维电子气的自旋轨道耦合强度的一个最有希望和广泛采取的方式，在实验上也易于实现。通过本项目实施，基于第一性原理计算，我们研究了在外加电场下, Bi2Se3类拓扑绝缘体薄膜的表面态，量子阱态的变化，自旋劈裂强度与电场大小之间的定量关系；研究了在Bi2Se3类拓扑绝缘体中的自旋劈裂中高阶Rashba项的贡献与外加电场之间的关系；研究了Bi2Se3类拓扑绝缘体与不同基底(石墨烯，Si)，或原子（Pb）构成的系统中界面态，量子阱态的变化，自旋劈裂的变化。另外，我们还研究了拓扑绝缘体Bi2Se3块体和薄膜中的层堆垛对其结构、电子态、拓扑态和自旋劈裂的影响。我们希望能为从原理上设计一些功能易为调控的新型自旋电子器件提供物理基础。