Non-Hermitian phase-biased Josephson junctions

TL;DR

This paper explores non-Hermitian Josephson junctions with phase bias, revealing topologically stable exceptional points that influence supercurrent behavior and could enhance device sensitivity.

Contribution

It introduces the concept of non-Hermitian effects in Josephson junctions, linking non-Hermitian topology with the Josephson effect for the first time.

Findings

Exceptional points occur at zero or finite energies depending on non-Hermiticity structure.

Supercurrents can diverge at exceptional points, indicating enhanced sensitivity.

Non-Hermitian topology influences the Josephson effect in novel ways.

Abstract

We study non-Hermitian Josephson junctions formed by superconductors with a finite phase difference under non-Hermiticity, which naturally appears due to coupling to normal reservoirs. Depending on the structure of non-Hermiticity, captured in terms of retarded self-energies, the low-energy spectrum hosts topologically stable exceptional points either at zero or finite real energies as a function of the superconducting phase difference. Interestingly, the corresponding phase-biased supercurrents may acquire divergent profiles at such exceptional points. This instance is a natural and unique non-Hermitian effect that signals a possible way to enhance the sensitivity of Josephson junctions. Our work opens a way for realizing unique non-Hermitian phenomena due to the interplay between non-Hermitian topology and the Josephson effect.