金属表面Rashba自旋轨道耦合作用研究进展

自旋轨道耦合是电子自旋与轨道相互作用的桥梁, 它提供了利用外电场来调控电子的轨道运动、进而调控电子自旋状态的可能. 固体材料中有很多有趣的物理现象, 例如磁晶各向异性、自旋霍尔效应、拓扑绝缘体等, 都与自旋轨道耦合密切相关. 在表面/界面体系中, 由于结构反演不对称导致的自旋轨道耦合称为Rashba自旋轨道耦合, 它最早在半导体材料中获得研究, 并因其强度可由栅电压灵活调控而备受关注, 成为电控磁性的重要物理基础之一. 继半导体材料后, 金属表面成为具有Rashba自旋轨道耦合作用的又一主流体系. 本文以Au(111), Bi(111), Gd(0001)等为例综述了磁性与非磁性金属表面Rashba自旋轨道耦合的研究进展, 讨论了表面电势梯度、原子序数、表面态波函数的对称性, 以及表面态中轨道杂化等因素对金属表面Rashba自旋轨道耦合强度的影响. 在磁性金属表面, 同时存在Rashba自旋轨道耦合作用与磁交换作用, 通过Rashba自旋轨道耦合可能实现电场对磁性的调控. 最后, 阐述了外加电场和表面吸附等方法对金属表面Rashba自旋轨道耦合的调控. 基于密度泛函理论的第一性原理计算和角分辨光电子能谱测量是金属表面Rashba自旋轨道耦合的两大主要研究方法, 本文综述了这两方面的研究结果, 对金属表面Rashba自旋轨道耦合进行了深入全面的总结和分析.

Recent progress in Rashba spin orbit coupling on metal surface

Spin-orbit coupling (SOC) is a bridge between the spin and orbital of an electron. Through SOC, spin of the electron can possibly be controlled throuth external electric fields. It is found that many novel physical phenomena in solids are related with SOC, for example, the magnetic anisotropy of magnetic materials, the spin Hall effect, and the topological insulator, etc. In the surface of solid or at the interface of heterostructure, Rashba SOC is induced by the structure inversion asymmetry. It was observed first in semiconductor heterostructure, which has an inversion asymmetric potential at the interface. Because Rashba SOC at the interface can be easily controlled through gate voltage, it is of great significance in the field of electric control of magnetism. Metal surface subsequent to semiconductor becomes another main stream with large Rashba SOC. In this paper, we review the recent progress in Rashba SOC in metal surfaces, including both the magnetic and nonmagnetic metal surfaces. We demonstrate the findings in Au(111), Bi(111), Gd(0001), etc., and discuss the possible factors that could influence Rashba SOC, including the surface potential gradient, atom number, the symmetry of the surface wavefunction, and the hybridization between the different orbitals in the surface states, etc. We also discuss the manipulation of Rashba SOC through electric field or surface decoration. In addition, on magnetic surface, there coexist Rashba SOC and magnetic exchange interaction, which provides the possibility of controlling magnetic properties by electric field through Rashba SOC. The angle-resolved photoemission spectroscopy and the first-principles calculations based on density functional theory are the two main methods to investigate the Rashba SOC. We review the results obtained by these two approaches and provide a thorough understanding of the Rashba SOC in metal surface.