Probing the helical edge states of a topological insulator by Cooper-pair injection

Abstract

We consider the proximity effect between a singlet $s$-wave superconductor and the edge of a quantum spin Hall (QSH) topological insulator. We establish that Andreev reflection at a QSH edge state/superconductor interface is perfect while nonlocal Andreev processes through the superconductor are totally suppressed. We compute the corresponding conductance and noise.