Magnetization of mesoscopic copper rings: Evidence for persistent currents

We have measured the low-temperature magnetization response of ${10}^7$ isolated mesoscopic copper rings to a slowly varying magnetic flux. At sufficiently low temperature, the total magnetization response oscillates as a function of the enclosed magnetic flux on the scale of half of a flux quantum. The amplitude of the oscillatory moment is ≊1.2×${10}^{\mathrm{-}15}$ ${\mathrm{Am}}^2$ and decreases exponentially with increasing temperature on the scale of the correlation energy ${\mathit{E}}_{\mathit{c}}$=hD/(2L${)}^2$≊80 mK. This is evidence for a flux-periodic persistent current in each ring of average value 3×${10}^{\mathrm{-}3}$e${\nu }_{\mathit{F}}$/L.