Effect of screening current induced pair breaking on magnetization of superconducting lead nanoparticles

Magnetization measurements on lead nanoparticles in the size range 35–45nm are presented. It is shown that the critical fields in these nanoparticles are enhanced significantly above their bulk values with temperature dependence also distinct from that of bulk. The observed “type II” like shape of the magnetization curves is explained on the basis of the Ginzburg–Landau phenomenology by invoking the pair breaking effect of the London screening currents, which makes the effective penetration depth an increasing function of the field. The temperature dependence of critical field is found to be consistent with our explanation.