Kinky Behavior in Josephson Junctions

TL;DR

This paper nonperturbatively studies a Josephson junction with an Anderson impurity, revealing a novel intermediate phase with a kink in energy and modified low-voltage I-V characteristics, extending previous perturbative results.

Contribution

It introduces a nonperturbative analysis of Josephson junctions with impurities, discovering a new intermediate phase with unique energy and current-voltage features.

Findings

Identification of a novel intermediate phase with a kink in energy.

Modification of low-voltage I-V characteristics due to the kink.

Confirmation of earlier perturbative results in a nonperturbative framework.

Abstract

We analyze nonperturbatively the behavior of a Josephson junction in which two BCS superconductors are coupled through an Anderson impurity. We recover earlier perturbative results which found that a $\delta=\pi$ phase difference is preferred when the impurity is singly occupied and the on-site Coulomb interaction is large. We find a novel intermediate phase in which one of $\delta=0$ and $\delta=\pi$ is stable while the other is metastable, with the energy $E(\delta)$ having a kink somewhere in between. As a consequence of the kink, the $I-V$ characteristics of the junction are modified at low voltages.