Fluctuation Superconductivity in Mesoscopic Aluminum Rings

TL;DR

This study investigates fluctuation-induced superconductivity in mesoscopic aluminum rings, demonstrating that thermal fluctuation theory accurately describes magnetic susceptibility measurements and highlighting the role of a single parameter in fluctuation behavior.

Contribution

The paper provides experimental validation of the exact fluctuation theory in mesoscopic superconducting rings and introduces a method to isolate magnetic signals at very high background flux.

Findings

Fluctuation theory matches experimental susceptibility data.

A single parameter characterizes fluctuation effects at suppressed critical temperatures.

Precise susceptibility measurements are achieved using a scanning SQUID.

Abstract

Fluctuations are important near phase transitions, where they can be difficult to describe quantitatively. Superconductivity in mesoscopic rings is particularly intriguing because the critical temperature is an oscillatory function of magnetic field. There is an exact theory for thermal fluctuations in one-dimensional superconducting rings, which are therefore expected to be an excellent model system. We measure the susceptibility of many rings, one ring at a time, using a scanning SQUID that can isolate magnetic signals from seven orders of magnitude larger background applied flux. We find that the fluctuation theory describes the results and that a single parameter characterizes the ways in which the fluctuations are especially important at magnetic fields where the critical temperature is suppressed.