Non-Hermitian superconducting diode effect

The study of nonreciprocal phenomena has long captivated interest in both Hermitian and non-Hermitian systems. The superconducting diode effect (SDE) is a nonreciprocal 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 an SDE in the non-Hermitian SQUID. We analyze the behavior of the SDE under both direct current and alternating current 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 avenues for investigating nonreciprocal phenomena in non-Hermitian systems.