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

A new description is proposed for the low-field critical behavior of type-II superconductors. The starting point is the Ginzburg-Landau theory in presence of an external magnetic field H. A set of fictitious vortex variables and a singular gauge transformation are used to rewrite a 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 vorticity. A possibility of a novel phase transition involving zero vorticity degrees of freedom and formation of a uniform condensate is suggested. A similarity to the superconducting [Higgs] electrodynamics and the nematic-smectic-A transition in liquid crystals is noted. The experimental situation is discussed. PACS 74.60.Ge Typeset using REVTEX