MULTIVORTEX STATES IN LARGE PINNING CENTERS

We have studied the vortex configurations in the large pinning centers i.e. in the spatial region with characteristic size a comparable with the London length lambda. It is shown that the type of configuration and the vortex number in the cluster are dependent on the ratio a/lambda and change nonmonotonically with temperature. The temperature region of the vortex configurations instability is obtained. The influence of vortex clusters on the decay of magnetization and current-voltage characteristics are discussed. The important role of the potential barrier for the penetration of vortices into the pinning center is shown. A new state of vortex cluster, "vortex polaron" is predicted. It is found that superconductivity is restored at a large external current.