Spontaneous Fluxoid Formation in Superconducting Loops

TL;DR

This paper experimentally verifies the Zurek-Kibble scenario in superconducting loops, demonstrating how fluxoid formation probability depends on quenching time and revealing a scaling exponent larger than theoretical predictions.

Contribution

First experimental verification of Zurek-Kibble scaling in superconducting rings across a wide parameter range, with analysis of the scaling exponent discrepancy.

Findings

Fluxoid formation probability follows allometric dependence on quenching time.

Observed Zurek-Kibble scaling exponent is 0.62±0.15, larger than expected.

Doubling of the exponent is explained for small loops assuming Gaussian winding number densities.

Abstract

We report on the first experimental verification of the Zurek-Kibble scenario in an isolated superconducting ring over a wide parameter range. The probability of creating a single flux quantum spontaneously during the fast normal-superconducting phase transition of a wide Nb loop clearly follows an allometric dependence on the quenching time $\tau_{Q}$, as one would expect if the transition took place as fast as causality permits. However, the observed Zurek-Kibble scaling exponent $\sigma = 0.62\pm0.15$ is two times larger than anticipated for large loops. Assuming Gaussian winding number densities we show that this doubling is well-founded for small annuli.