Vortex configurations in a Pb/Cu microdot with a 2x2 antidot cluster
  We present a detailed study of the transport properties of a superconducting Pb/Cu microdot with a 2x2 antidot cluster. The superconducting-normal (S/N) phase boundary, critical currents and current-voltage characteristics of this structure have been measured. The S/N phase boundary as a function of field B (T_c(B)) reveals an oscillatory structure caused by the limited number of possible vortex configurations which can be realized in these small clusters of pinning centres (antidots). We have analyzed the stability of these configurations and discussed the possible dissipation mechanisms using the critical current (J_c(B)) and voltage-current (V(I)) characteristics data. A comparison of the experimental data of T_c(B) and J_c(B) with calculations in the London limit of the Ginzburg-Landau theory confirms that vortices can indeed be pinned by the antidots forming a cluster and that the ground-state configurations of the vortices are noticeably modified by sending current through the structure. The possibility of generating phase-slips as well as motion of the vortices in the 2x2 antidot cluster has also been discussed. 
T. Puig, E. Rosseel, L. Van Look, M.J. Van Bael, V.V. Moshchalkov, Y.   Bruynseraede, R. Jonckheere