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 \ensuremath{\approxeq}1.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}15}$ ${\mathrm{Am}}^{2}$ and decreases exponentially with increasing temperature on the scale of the correlation energy ${\mathit{E}}_{\mathit{c}}$=hD/(2L${)}^{2}$\ensuremath{\approxeq}80 mK. This is evidence for a flux-periodic persistent current in each ring of average value 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$e${\ensuremath{\nu}}_{\mathit{F}}$/L.