Nucleation of superconductivity in an overcooled normal domain

Relaxation of the overcooled normal domain with magnetic flux in type-I and type-II superconductors is considered. Two regimes of dynamics, depending on the domain size and the amount of trapped magnetic flux have been found: decay into single vortices and explosive nucleation of the topological vor tices and antivortices. Small overcooled normal spots in type-II supercondu ctors decay into a cluster of Abrikosov vortices while the restoration of s uperconductivity in large domains with weak magnetic fields leads to the cr eation of a long-living vortex-antivortex mixed state. In the presence of p inning centers in the sample this state can be frozen and persist indefinit ely, Application of a week external magnetic field extracts antivortices fr om the sample thus causing net increase of the magnetic penetrating into th e sample. (C) 2000 Elsevier Science B.V. All rights reserved.