Topological surface states of Bi₂Se₃ coexisting with Se vacancies

Although topological surface states are known to be robust against nonmagnetic surface perturbations, their band dispersions and spatial distributions are still sensitive to surface defects. Taking Bi₂Se₃ as an example, we demonstrate that Se vacancies modify the surface band structures considerably. When large numbers of Se vacancies exist on the surface, topological surface states may sink down from the first to the second quintuple layer and get separated from the vacancies. We simulated scanning tunnelling microscopy images to distinguish surfaces with Se and Bi terminations.