Magnetic response of a single, isolated gold loop

Measurements have been made of the low-temperature magnetic response of single, isolated, micron-size Au loops. The magnetic response is found to contain a component which oscillates with the applied magnetic flux with a fundamental period of ${\mathrm{\Phi }}_0$=h/e. The amplitude of the oscillatory component corresponds to a persistent current of ≃(0.3–2.0)${\mathit{ev}}_{\mathit{F}}$/L, 1 to 2 orders of magnitude larger than predicted by current theories.