The Superconductivity of the Topologically Protected Surface States of Bi${}_2$Se${}_3$: Experiment

Placing a 3D topological insulator (TI) in proximity to an s-wave superconductor (S) is predicted to induce 2D p-wave superconductivity into the topologically-protected surface state (TSS). The details of the TI/S interface are critical for the search for Majorana bound states in these systems. In this talk, we will present cryogenic scanning tunneling microscopy measurements of Bi${}_2$Se${}_3$ with nanometer scale islands of Nb and PbBi deposited on the surface. Local density of states measurements are consistent with superconductivity in the top quintuple layer, with a coherence length of about 500 nm. Moreover, we find clear evidence of a reverse proximity effect for which the TSS from the TI leaks back into the local density of states measured on the superconducting islands.