Breakdown of the superheated Meissner state and spontaneous vortex nucleation in type II superconductors

The theory of local stability of the superheated Meissner state presented in an earlier paper is supplemented by an investigation of global stability in two dimensions. We conclude that flux penetration cannot be delayed beyond the fieldH _s1 where local instability sets in. Various new two-dimensional Ginzburg-Landau solutions, obtained numerically, are discussed. These include the lowest saddle point separating the Meissner from the normal and vortex state and a solution resembling the “nascent vortex state” whose existence was postulated recently by Walton and Rosenblum. Using these solutions the process of spontaneous vortex nucleation is discussed.