Scanning tunneling microscopy of superconducting topological surface states in Bi${}_2$Se${}_3$

In this paper we present scanning tunneling microscopy of a large ${\text{Bi}}_2{\text{Se}}_3$ crystal with superconducting PbBi islands deposited on the surface. Local density of states measurements are consistent with induced superconductivity in the topological surface state with a coherence length of order 540 nm. At energies above the gap the density of states exhibits oscillations due to scattering caused by a nonuniform order parameter. Strikingly, the spectra taken on islands also display similar oscillations along with traces of the Dirac cone, suggesting an inverse topological proximity effect.