Dresden 2014 – scientific programme

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O: Fachverband Oberflächenphysik

O 42: Topological Insulators: Theory (HL jointly with MA, O, TT)

O 42.6: Talk

Wednesday, April 2, 2014, 10:45–11:00, POT 151

Electronic properties of the topological crystalline insulator SnTe and its (001) and (111) surfaces: an ab-initio study — •Matthias Drüppel, Peter Krüger, and Michael Rohlfing — Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster

The insulator SnTe belongs to the recently discovered class of materials in which a crystalline symmetry ensures the existence of topologically protected surface states. We report on the properties of these states at the (001) and (111) surfaces. To this end, we have employed density-functional theory.

The bulk band structure of SnTe is characterized by inversion at the four equivalent L points giving rise to a mirror Chern number n_m = − 2. The (001) surface exhibits two mirror planes and shows four Dirac cones at non-time-reversal-invariant points along the ± ΓX and ± ΓX′ lines, respectively. Here we explore the influence of lattice deformations on the stability of the surface states. Our results reveal that distortions of the topmost layers which break a mirror symmetry locally at the surface do not lead to an opening of the surface band gap. We find that onlybulk lattice deformations, e.g. rhombohedrial distortions, that break one or both mirror symmetries also in the bulk part of the system give rise to a surface band gap. Our calculations show that the Sn terminated (111) surface exhibits Dirac cones centered at Γ and M. In particular at the M point, these topologically protected states are distinctly extended into the bulk. Interestingly, we observe for the Te terminated (111) surface a gap-closing Dirac state only at the Γ point