Theory of Microwave-Assisted Supercurrent in Diffusive SNS Junctions

TL;DR

This paper develops a theoretical model explaining the microwave-induced enhancement of supercurrent in diffusive SNS junctions, attributing it to quasiparticle energy redistribution caused by electromagnetic fields.

Contribution

It introduces a quasiclassical Green's function-based theory that explains the microwave enhancement of supercurrent in diffusive SNS junctions, covering various conditions.

Findings

Critical current enhancement explained by quasiparticle energy redistribution.

Theory matches experimental observations across temperature and frequency ranges.

Provides detailed predictions for current-phase relationships under microwave irradiation.

Abstract

The observation of very large microwave-enhanced critical currents in superconductor-normal metal-superconductor (SNS) junctions at temperatures well below the critical temperature of the electrodes has remained without a satisfactory theoretical explanation for more than three decades. Here we present a theory of the supercurrent in diffusive SNS junctions under microwave irradiation based on the quasiclassical Green's function formalism. We show that the enhancement of the critical current is due to the energy redistribution of the quasiparticles in the normal wire induced by the electromagnetic field. The theory provides predictions across a wide range of temperatures, frequencies, and radiation powers, both for the critical current and the current-phase relationship.