Transitions between different superconducting states in mesoscopic disks

Using a linear analysis, we study the stability of giant-vortex states in very thin disks. The vortex expulsion and penetration fields are obtained for finite thickness disks from a numerical solution of the non-linear Ginzburg-Landau (GL) equations. Using an extension of the London approximation, in which the phase distribution of the order parameter is prescribed and the superconducting electron density is found numerically, we consider the free energy behavior for transitions between different superconducting states.