Vortex shells in mesoscopic superconducting disks

The distribution of vortices over different vortex shells in mesoscopic superconducting disks with sufficiently large sizes is investigated within the framework of the nonlinear Ginzburg-Landau theory. Keeping the total vorticity fixed, different vortex configurations can be found in which the vortices are distributed differently over the vortex shells. An overview is given of the different possible vortex configurations and the free energies of these states are compared. In general, the difference in the free energy between the possible vortex configurations with the same vorticity is much smaller than the difference in the free energy between vortex states with different vorticity. The transitions between different vortex states with the same and different vorticity are investigated. Contrary to small disks, the change in vorticity can be larger than one with increasing and decreasing magnetic field. Also a combination of a giant vortex state with a multivortex state can nucleate into a stable vortex state. The influence of the sample thickness is briefly studied. Our results are compared with those obtained from the London approximation which clearly shows the limited applicability of the latter.