College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007, People's Republic of China.
J Phys Condens Matter. 2013 Jul 3;25(26):265005. doi: 10.1088/0953-8984/25/26/265005. Epub 2013 Jun 13.
The effects of S atom surface adsorption and substitution on the helical surface states of Sb2Te3 are studied by the density-functional theory with spin-orbit coupling being taken into account self-consistently. It is found that S atoms play the role of surface passivation when adsorbed on both surfaces of a 6QL Sb2Te3 film in symmetrical configuration. For symmetrical surfaces with both the top and bottom surfaces of a thin film with adsorbed S atoms, the linear dispersion of the surface states is found to be preserved and the topological surface states survive. The spatial distribution of charge density of the surface state at the Γ[overline] point is also symmetric. For a film with asymmetric S atom adsorption, i.e., only one of the surfaces has adsorbed S atoms, the surface band structure is found to be very different. The degeneracy of the surface states from the two sides of a film is broken. The gap opens slightly at Γ[overline] and the spatial distribution of charge density of the surface state at the Γ[overline] point is also modified greatly. The Fermi level is robust against S impurity adsorption on the surface of Sb2Te3. Compared with S substitution, the effect of single surface S adsorption on electron structures is more prominent. This supports the idea that the topological insulator surface electronic states are dominated by its structural symmetry and the effect of the asymmetric environment of topological insulator Sb2Te3 films should thus be considered.
通过考虑自旋轨道耦合的自洽密度泛函理论，研究了 S 原子表面吸附和取代对 Sb2Te3 螺旋表面态的影响。研究发现，当 S 原子以对称构型吸附在 Sb2Te3 薄膜的两个表面上时，S 原子起到表面钝化的作用。对于具有吸附 S 原子的薄膜的顶表面和底表面都对称的表面，发现表面态的线性色散得以保持，拓扑表面态得以幸存。Γ[overline]点处表面态的电荷密度空间分布也是对称的。对于 S 原子吸附不对称的薄膜，即只有一个表面吸附了 S 原子，发现表面能带结构非常不同。薄膜两侧的表面态简并被打破。Γ[overline]处的能隙略有打开，Γ[overline]点处表面态的电荷密度空间分布也发生了很大的改变。费米能级对 Sb2Te3 表面的 S 杂质吸附具有很强的鲁棒性。与 S 取代相比，单个表面 S 吸附对电子结构的影响更为显著。这支持了拓扑绝缘体表面电子态主要由其结构对称性决定的观点，因此应该考虑拓扑绝缘体 Sb2Te3 薄膜不对称环境的影响。
