Persistent currents in normal metal rings

TL;DR

This study measures persistent currents in individual gold rings, confirming theoretical predictions for amplitude and temperature dependence, and highlighting variability and discrepancies with previous experiments.

Contribution

First direct measurement of persistent currents in individual gold rings, validating diffusive ring theory and revealing variability among rings.

Findings

Measured flux periodic response in small gold rings

Amplitude distribution matches diffusive ring predictions

Temperature dependence aligns with theoretical models

Abstract

The authors have measured the magnetic response of 33 individual cold mesoscopic gold rings, one ring at a time. The response of some sufficiently small rings has a component that is periodic in the flux through the ring and is attributed to a persistent current. Its period is close to h/e, and its sign and amplitude vary between rings. The amplitude distribution agrees well with predictions for the typical h/e current in diffusive rings. The temperature dependence of the amplitude, measured for four rings, is also consistent with theory. These results disagree with previous measurements of three individual metal rings that showed a much larger periodic response than expected. The use of a scanning SQUID microscope enabled in situ measurements of the sensor background. A paramagnetic linear susceptibility and a poorly understood anomaly around zero field are attributed to defect spins.