Role of surface passivation in the formation of Dirac states at polar surfaces of topological crystalline insulators: The case of SnTe(111)

We present ab initio density functional theory (DFT) calculation results for electronic and spin structures of both the Te- and Sn-terminated SnTe(111) polar surfaces. Rocksalt narrow-gap semiconductor SnTe belongs to the recently discovered class of topological crystalline insulators in which the topological nature of surface electronic states arises from the crystal symmetry combined with band inversion at the $L$ point. We demonstrate that in contrast to earlier model calculations only trivial spin-split states propagating over the entire two-dimensional Brillouin zone emerge at the SnTe(111) surfaces owing to the surface potential effect which destroys weakly protected topological states. We show that the surface passivation eradicates the trivial surface states and recovers the even number of the helical spin-polarized topological Dirac cones centered at the $\overline{\ensuremath{\Gamma}}$ and $\overline{\mathrm{M}}$ points prescribed for the topological crystalline insulator by the crystal symmetry.