Pair-breaking effect on mesoscopic persistent currents

We consider the contribution of superconducting fluctuations in the mesoscopic persistent current (PC) of an ensemble of normal metallic rings, made of a superconducting material whose low bare transition temperature Tc0 is much smaller than the Thouless energy Ec. The effect of pair breaking is introduced via the example of magnetic impurities. We find that over a rather broad range of pair-breaking strength / τs, such that Tc0 / τs Ec, the superconducting transition temperature is normalized down to minute values or zero while the PC is hardly affected. This may provide an explanation for the magnitude of the average PCs in copper and gold as well as a way to determine their Tc0 's. The dependence of the current and the dominant superconducting fluctuations on Ec τs and on the ratio between Ec and the temperature is analyzed. The measured PCs in copper (gold) correspond to Tc0 of a few (a fraction of) mK.