Magnetization of mesoscopic copper rings: Evidence for persistent currents

We have measured the low-temperature magnetization response of 10⁷ 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^-15 Am² and decreases exponentially with increasing temperature on the scale of the correlation energy Ec=hD/(2L)²{}80 mK. This is evidence for a flux-periodic persistent current in each ring of average value 3×{}10^-3eνF/L.