Probing the Superconducting Proximity Effect of Topological Insulator $\textrm{Bi}_2\textrm{Se}_3$ Using Scanning Tunneling Microscopy

Placing a 3D topological insulator (TI) in proximity to an s-wave superconductor is theoretically predicted to induce 2D p-wave superconductivity into the topologically protected surface state (TSS). In this talk, we will present cryogenic scanning tunneling microscopy measurements of a large $\textrm{Bi}_2\textrm{Se}_3$ crystal with nanometer scale islands of PbBi deposited on the surface. Local density of states measurements are consistent with p-wave superconductivity in the top $\textrm{Bi}_2\textrm{Se}_3$ quintuple layer, with coherence length of $540 \pm 50$ nm in the direction parallel to the layer. We see indications of a reverse proximity effect as well, where the TSS from the TI leaks back into local density of states measured on the superconducting islands. The density of states curves also exhibit structure which we interpret as McMillan-Rowell oscillations due to Andreev confinement perpendicular to the layer.