Inelastic helium atom scattering from SbTe(111): phonon dispersion, focusing effects and surfing.

We present an experimental study of inelastic scattering processes on the (111) surface of the topological insulator SbTe using helium atom scattering. In contrast to other binary topological insulators such as BiSe and BiTe, SbTe is much less studied and the as-grown SbTe sample turns out to be p-doped, with the Fermi-level located below the Dirac-point as confirmed by angle-resolved photoemission spectroscopy. We report the surface phonon dispersion along both high symmetry directions in the energy region below 11 meV, where the Rayleigh mode exhibits the strongest intensity.