Formation of superconducting phase nuclei at defects

The problem of the origination of a superconducting nucleus in an external magnetic field for type I superconductors is considered in a pure crystal and in a crystal containing point defects, in the specimen bulk and on the surface. The shape of the nucleus, the energy barriers to nucleus formation, and the changes in the critical fields with the concentrations of defects are found. It is shown that the presence of defect clumps of the necessary sign in the crystal (of dilatation center type) makes possible the existence of a superconducting fluctuon in this group of defects. The range of parameters for fluctuon existence is determined and it is shown that the unusual behavior observed in contaminated aluminum at a n−s transition can be explained by the formation of a superconducting fluctuon.

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