Microscopic simulation of superconductor-topological insulator proximity structures

TL;DR

This paper provides a microscopic, self-consistent analysis of the superconducting proximity effect at a superconductor-topological insulator interface, revealing induced triplet correlations and validating the Fu-Kane model with renormalized parameters.

Contribution

It offers the first self-consistent microscopic calculations of the proximity effect, including the order parameter suppression and triplet pairing, and extracts phenomenological parameters for the Fu-Kane model.

Findings

Triplet correlations with p_x ± i p_y symmetry are induced at the interface.

The sub-gap spectrum matches the Fu-Kane model predictions.

Phenomenological parameters are strongly renormalized from bulk values.

Abstract

We present microscopic, self-consistent calculations of the superconducting order parameter and pairing correlations near the interface of an $s$-wave superconductor and a three-dimensional topological insulator with spin-orbit coupling. We discuss the suppression of the order parameter by the topological insulator and show that the equal-time pair correlation functions in the triplet channel, induced by spin-flip scattering at the interface, are of $p_x\pm i p_y$ symmetry. We verify that the spectrum at sub-gap energies is well described by the Fu-Kane model. The sub-gap modes are viewed as interface states with spectral weight penetrating well into the superconductor. We extract the phenomenological parameters of the Fu-Kane model from microscopic calculations, and find they are strongly renormalized from the bulk material parameters. This is consistent with previous results of Stanescu et al for a lattice model using perturbation theory in the tunneling limit.