Dispersion of the surface phonons in semiconductor/topological insulator Si/BiTe heterostructure studied by high resolution Brillouin spectroscopy.

The dynamics and dispersion of surface phonons in heterostructure semiconductor/ topological insulator Si/BiTe was investigated using high resolution Brillouin light scattering method in the GHz frequency range. Both Rayleigh and Sezawa surface acoustic waves have been observed for wave vectors ranging from 0.006 to 0.023 nm. Anomaly in dispersion relations ω(q) for both surface waves were detected for the wave vector q = 0.016 nm. The finite element method (FEM) was used to simulate the observed shapes of ω(q) and to find the deformation profiles of surface acoustic waves. We attribute the observed changes to the coupling between low energy electrons and surface phonons. The coupling between helical Dirac states and surface phonons is discussed in the frame of accessible theoretical models.