The helical surface states of the S-covered topological insulator Sb₂Te₃(0001)

Author： Zhao Xu Dai Xian-Qi Zhao Bao Wang Ning Ji Yuan-Yuan

ISSN： 0953-8984

Source： Journal of Physics: Condensed Matter, Vol.25, Iss.26, 2013-07, pp. : 265005-265010

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Abstract

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 &$bar {Gamma }$; 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 &$bar {Gamma }$; and the spatial distribution of charge density of the surface state at the &$bar {Gamma }$; 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.