Critical fields of mesoscopic superconductors

Recent measurements have shown oscillations in the upper critical field of simply connected mesoscopic superconductors. A quantitative theory of these effects is given here on the basis of a Ginzburg-Landau description. I;or small fields, the H - T phase boundary exhibits a cusp where the screening currents change sign for the first time thus defining a lower critical field H-c1. In the limit where many flux quanta are threading the sample, nucleation occurs at the boundary and the upper critical field becomes identical with the surface critical field H-c3.