# Dresden 2014 – wissenschaftliches Programm

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# HL: Fachverband Halbleiterphysik

## HL 59: Topological insulators: Theory (with MA/O/TT)

### HL 59.6: Vortrag

### Mittwoch, 2. April 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 only*bulk* 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