Andreev reflection in two-dimensional topological insulators with either conserved or broken time-reversal symmetry

TL;DR

This paper studies Andreev reflection in 2D topological insulators with and without time-reversal symmetry, revealing robustness and edge state effects, and proposes an experimental method to distinguish these phases.

Contribution

It demonstrates perfect Andreev reflection in both classes of topological insulators and proposes a novel experimental approach to differentiate them without band structure measurement.

Findings

Perfect Andreev reflection is robust against disorder in both cases.

Magnetic impurities suppress one Andreev channel only in time-reversal symmetric insulators.

A tabletop experiment can distinguish topological insulator types without direct band structure measurement.

Abstract

We investigate Andreev reflection in two-dimensional heterojunctions formed by a superconductor in contact with a topological insulator ribbon either possessing or breaking time-reversal symmetry. Both classes of topological insulators exhibit perfect Andreev reflection, which is robust against disorder. This is assigned to topologically protected edge states. In the time-reversal symmetric case we show that doping one of the ribbon edges with magnetic impurities suppresses one Andreev channel, while no such suppression is seen in the broken symmetry situation. Based on this observation we suggest a tabletop transport experiment able to distinguish between the two types of topological insulators, which does not involve the direct measurement of the material band structure.