Enhancement of the retrapping current of superconducting microbridges of finite length

TL;DR

This paper theoretically demonstrates that suppressing the order parameter in attached leads can increase the retrapping current in superconducting microbridges, explaining experimental observations of enhanced critical currents and negative magnetoresistance.

Contribution

It introduces a novel theoretical insight into how the suppression of the order parameter in leads affects the retrapping current in microbridges, with implications for understanding experimental phenomena.

Findings

Resistance decreases while retrapping current increases with order parameter suppression.

Effect is absent in short microbridges and weak in long ones.

Nonmonotonous dependence of retrapping current on microbridge length predicted.

Abstract

We theoretically find that the resistance of a superconducting microbridge/nanowire {\it decreases} while the retrapping current $I_r$ for the transition to the superconducting state {\it increases} when one suppresses the magnitude of the order parameter $|\Delta|$ in the attached superconducting leads. This effect is a consequence of the increased energy interval for diffusion of the 'hot' nonequilibrium quasiparticles (induced by the oscillations of $|\Delta|$ in the center of the microbridge) to the leads. The effect is absent in short microbridges (with length less than the coherence length) and it is relatively weak in long microbridges (with length larger than the inelastic relaxation length of the nonequilibrium distribution function). A nonmonotonous dependence of $I_r$ on the length of the microbridge is predicted. Our results are important for the explanation of the enhancement of the critical current and the appearance of negative magnetoresistance observed in many recent experiments on superconducting microbridges/nanowires.