Low-magnetic-field critical behavior in strongly type-II superconductors.

Abstract

A description is proposed for the low-field critical behavior of type-II superconductors. The starting point is the Ginzburg-Landau functional in presence of an external magnetic field H. A set of fictitious vortex variables and a singular gauge transformation are used to rewrite this finite H Ginzburg-Landau functional in terms of a complex scalar field of zero average vorticity. The continuum limit of the transformed problem takes the form of an H=0 Ginzburg-Landau functional for a charged field coupled to a fictitious ``gauge'' potential, which arises from long-wavelength fluctuations in the background liquid of field-induced vortices. A possibility of a phase transition involving zero-vorticity degrees of freedom and formation of a uniform condensate is suggested. A similarity with the superconducting (Higgs) electrodynamics and the nematic-smectic-A transition in liquid crystals is noted. The experimental situation is discussed.