Cooper-Pair Injection into Quantum Spin Hall Insulators

TL;DR

This paper theoretically investigates how Cooper pairs tunnel from a superconductor into the edge states of a two-dimensional topological insulator, revealing entanglement and fractionalization effects in electron transport.

Contribution

It introduces a model for Cooper pair tunneling into helical edge states, highlighting the role of spin pairing and electron fractionalization in topological insulators.

Findings

Positive current cross correlations due to Cooper pair tunneling

Spin pairing influences Cooper pair partitioning into edge states

Electron fractionalization leads to charge pulses with fractional charge

Abstract

We theoretically study tunneling of Cooper pairs from a superconductor spanning a two-dimensional topological insulator strip into its helical edge states. The coherent low-energy electron-pair tunneling sets off positive current cross correlations along the edges, which reflect an interplay of two quantumentanglement processes. Most importantly, superconducting spin pairing dictates a Cooper pair partitioning into the helical edge liquids, which transport electrons in opposite directions for opposite spin orientations. At the same time, Luttinger-liquid correlations fractionalize electrons injected at a given edge into counterpropagating charge pulses carrying definite fractions of the elementary electron charge.