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 vortices and antivortices. Small overcooled normal spots in type-II superconductors decay into a cluster of Abrikosov vortices while the restoration of superconductivity in large domains with weak magnetic fields leads to the creation of a long-living vortex-antivortex mixed state. In the presence of pinning centers in the sample this state can be frozen and persist indefinitely. Application of a week external magnetic field extracts antivortices from the sample thus causing net increase of the magnetic penetrating into the sample.