Non-equilibrium Josephson effect through helical edge states

TL;DR

This paper investigates the fractional Josephson effect in topological insulator-based junctions, revealing signatures in current noise and Majorana bound states, advancing understanding of non-equilibrium phenomena in topological superconductivity.

Contribution

It demonstrates how finite-frequency current noise can reveal the fractional Josephson effect and discusses Majorana bound states at superconductor edges in topological insulators.

Findings

Signatures of fractional Josephson effect observed in current noise.

Majorana bound states identified at superconductor edges.

4Pi-periodic Andreev bound states confirmed.

Abstract

We study Josephson junctions between superconductors connected through the helical edge states of a two-dimensional topological insulator in the presence of a magnetic barrier. As the equilibrium Andreev bound states of the junction are 4Pi-periodic in the superconducting phase difference, it was speculated that, at finite dc bias voltage, the junction exhibits a fractional Josephson effect with half the Josephson frequency. Using the scattering matrix formalism, we show that signatures of this effect can be seen in the finite-frequency current noise. Furthermore, we discuss other manifestations of the Majorana bound states forming at the edges of the superconductors.