Vortex-induced dissipation in narrow current-biased thin-film superconducting strips

TL;DR

This paper investigates vortex crossings in narrow superconducting strips, linking vortex-induced dissipation to dark counts in photon detectors, and provides estimates for crossing rates and voltage pulse characteristics.

Contribution

It introduces a model connecting vortex crossings to dissipation and dark counts, with quantitative estimates matching experimental data.

Findings

Vortex crossings cause detectable voltage pulses in superconducting strips.

Hot vortex crossings are linked to dark counts in photon detectors.

Estimated vortex crossing rates align with experimental observations.

Abstract

A vortex crossing a thin-film superconducting strip from one edge to the other, perpendicular to the bias current, is the dominant mechanism of dissipation for films of thickness d on the order of the coherence length XI; and of width w much narrower than the Pearl length LAMBDA >> w >> XI. At high bias currents, I* < I < Ic, the heat released by the crossing of a single vortex suffices to create a belt-like normal-state region across the strip, resulting in a detectable voltage pulse. Here Ic is the critical current at which the energy barrier vanishes for a single vortex crossing. The belt forms along the vortex path and causes a transition of the entire strip into the normal state. We estimate I* to be roughly Ic/3. Further, we argue that such "hot" vortex crossings are the origin of dark counts in photon detectors, which operate in the regime of metastable superconductivity at currents between I* and Ic. We estimate the rate of vortex crossings and compare it with recent experimental data for dark counts. For currents below I*, i.e., in the stable superconducting but resistive regime, we estimate the amplitude and duration of voltage pulses induced by a single vortex crossing.