Diode effects in current-biased Josephson junctions

TL;DR

This paper develops a theory explaining diode-like effects in Josephson junctions, attributing asymmetries in switching and retrapping currents to different microscopic mechanisms, with implications for identifying their origins.

Contribution

It introduces a comprehensive theory distinguishing the microscopic origins of diode effects in switching and retrapping currents in Josephson junctions.

Findings

Diode-like switching currents arise from asymmetric current-phase relations.

Nonreciprocal retrapping currents are due to asymmetric quasiparticle currents.

The theory is exemplified with a model involving a magnetic atom in the junction.

Abstract

Current-biased Josephson junctions exhibit hysteretic transitions between dissipative and superconducting states as characterized by switching and retrapping currents. Here, we develop a theory for diode-like effects in the switching and retrapping currents of weakly-damped Josephson junctions. We find that while the diode-like behavior of switching currents is rooted in asymmetric current-phase relations, nonreciprocal retrapping currents originate in asymmetric quasiparticle currents. These different origins also imply distinctly different symmetry requirements. We illustrate our results by a microscopic model for junctions involving a single magnetic atom. Our theory provides significant guidance in identifying the microscopic origin of nonreciprocities in Josephson junctions.