Unpaired vortices and layer decoupling in quasi-two-dimensional superconductors: A model calculation

Abstract

Layer decoupling, as a consequence of interlayer phase fluctuations, is studied in Josephson-coupled, layered superconductors for the case of no external magnetic field. At temperatures slightly above the thermodynamic transition temperature Tc, the weakening of interlayer phase coherence is primarily due to dissociated (‘‘free’’) pancake vortices which are similar to those of the two-dimensional theory. A model is proposed to account for these fluctuations in a layered system. The model is approximately solved using a self-consistent, mean-field method to incorporate fluctuation effects into the renormalized Josephson coupling. The renormalized Josephson parameter λ̃J, which describes the ability of neighboring layers to expel the interlayer phase fluctuations between them, is found to diverge at a distinct temperature Tcc>Tc, signifying that the layers become decoupled. The asymmetry of the phase transition around Tc, brought about by layer decoupling, is discussed. In particular, the three-dimensional region above Tc is shown to be compressed.

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