Proximity effect at the superconductor–topological insulator interface

Abstract

We study the excitation spectrum of a topological insulator in contact with an $s$-wave superconductor, starting from a microscopic model, and develop an effective low-energy model for the proximity effect. In the vicinity of the Dirac cone vertex, the effective model describing the states localized at the interface is well approximated by a model of Dirac electrons experiencing superconducting $s$-wave pairing. Away from the cone vertex, the induced pairing potential develops a $p$-wave component with a magnitude sensitive to the structure of the interface. Observing the induced $s$-wave superconductivity may require tuning the chemical potential close to the Dirac point. Furthermore, we find that the proximity of the superconductor leads to a significant renormalization of the original parameters of the effective model describing the surface states of a topological insulator.