Decay of near-critical currents in superconducting nanowires

TL;DR

This paper investigates the decay mechanisms of supercurrents in superconducting nanowires, explaining the observed power-3/2 activation barrier scaling and analyzing quantum tunneling effects near the critical current.

Contribution

It introduces a discrete model for superconducting nanowires that captures the power-3/2 thermal activation scaling and explores quantum phase slip tunneling with a new power-5/4 scaling law.

Findings

Power-3/2 scaling of activation barrier in discrete model

Quantum tunneling exhibits power-5/4 scaling near critical current

Scaling laws hold for both long and short wires with leads

Abstract

We consider decay of supercurrent via phase slips in a discrete one-dimensional superconductor (a chain of nodes connected by superconducting links), aiming to explain the experimentally observed power-3/2 scaling of the activation barrier in nanowires at currents close to the critical. We find that, in this discrete model, the power-3/2 scaling holds for both long and short wires even in the presence of bulk superconducting leads, despite the suppression of thermal fluctuations at the ends. We also consider decay via tunneling (quantum phase slips), which becomes important at low temperatures. We find numerically the relevant Euclidean solutions (periodic instantons) and determine the scaling of the tunneling exponent near the critical current. The scaling law is power-5/4, different from that of the thermal activation exponent.