Evidence for Thermally Activated Spontaneous Fluxoid Formation in Superconducting Thin-Film Rings

TL;DR

This study demonstrates spontaneous fluxoid formation in superconducting Mo3Si rings during cooling, explained by thermally activated fluxoid freezout, offering insights into fluxoid dynamics beyond causality-based models.

Contribution

It provides experimental evidence for thermally activated fluxoid formation in superconducting rings and introduces a model involving vortex transport as a new mechanism.

Findings

Fluxoids form spontaneously during cooling.

Fluxoid formation depends on quench rate and magnetic field.

The freezout model explains observed fluxoid behavior.

Abstract

We have observed spontaneous fluxoid generation in thin-film rings of the amorphous superconductor Mo$_3$Si, cooled through the normal-superconducting transition, as a function of quench rate and externally applied magnetic field, using a variable sample temperature scanning SQUID microscope. Our results can be explained using a model of freezout of thermally activated fluxoids, mediated by the transport of bulk vortices across the ring walls. This mechanism is complementary to a mechanism proposed by Kibble and Zurek, which only relies on causality to produce a freezout of order parameter fluctuations.