Josephson current via an isolated Majorana zero mode

TL;DR

This paper investigates how Majorana zero modes influence the Josephson current in superconductor junctions, revealing signatures like anomalous supercurrents that could help identify Majorana states in experiments.

Contribution

It demonstrates that breaking time-reversal symmetry enables Majorana contributions to the supercurrent and predicts an anomalous supercurrent at zero phase difference as a Majorana signature.

Findings

Majorana modes enable supercurrent transfer in superconductor junctions.

Breaking time-reversal symmetry activates Majorana contributions.

Anomalous supercurrent occurs at zero phase difference due to Majoranas.

Abstract

We study the equilibrium dc Josephson current in a junction between an $s$-wave and a topological superconductor. Cooper pairs from the $s$-wave superconducting lead can transfer to the topological side either via an unpaired Majorana zero mode localized near the junction, or via the above-gap continuum states. We find that the Majorana contribution to the supercurrent can be switched on when time-reversal symmetry in the conventional lead is broken, e.g., by an externally applied magnetic field inducing a Zeeman splitting. Moreover, if the magnetic field has a component in the direction of the effective spin-orbit field, there will be a Majorana-induced anomalous supercurrent at zero phase difference. This behavior may serve as a signature characteristic of Majorana zero modes, and is accessible to devices with only superconducting contacts.