Non-Hermitian superconducting diode effect

TL;DR

This paper introduces a non-Hermitian superconducting diode effect in a SQUID system, demonstrating how non-Hermiticity via phase decoherence can induce non-reciprocal supercurrents and asymmetric phenomena, expanding understanding of non-reciprocal effects.

Contribution

The study presents the first demonstration of a non-Hermitian superconducting diode effect driven by phase decoherence in a SQUID, revealing new mechanisms for non-reciprocal superconducting phenomena.

Findings

Non-Hermitian SDE can be realized in a SQUID with phase decoherence.

Direction-dependent critical currents and asymmetric Shapiro steps observed.

Emergent non-Hermitian Fermi-Dirac distribution induces SDE.

Abstract

The study of non-reciprocal phenomena has long captivated interest in both Hermitian and non-Hermitian systems. The superconducting diode effect (SDE) is a non-reciprocal phenomenon characterized by unequal critical charge supercurrents flowing in opposite directions in Hermitian superconducting systems. In this study, we introduce an SDE driven by non-Hermiticity in a superconducting quantum interference device (SQUID) under an external magnetic flux, which we refer to as the non-Hermitian SDE. Non-Hermiticity is introduced by coupling one of the two Josephson junctions to a gapless electron reservoir, introducing phase decoherence. Remarkably, we find that an emergent non-Hermitian Fermi-Dirac distribution can give rise to SDE in the non-Hermitian SQUID. We analyze the behavior of the SDE under both direct current (dc) and alternating current (ac) biases, highlighting the appearance of direction-dependent critical currents and asymmetric Shapiro steps as hallmarks of the SDE. Our findings not only reveal an experimentally accessible mechanism for non-Hermitian SDE but also open new avenues for investigating non-reciprocal phenomena in non-Hermitian systems.