Critical fluctuations and disorder at the vortex liquid to crystal transition in type-II superconductors.

Abstract

We present a functional renormalization group (FRG) analysis of a Landau-Ginzburg model of type-II superconductors (generalized to $n/2$ complex fields) in a magnetic field, for both a pure and a disordered system. The disordered system supports a stable FRG fixed point for $1<n<4$, identical to that of the disordered $O(n)$ model in $d\ensuremath{-}2$ dimensions. The pure system has a stable fixed point only for $n>4$ indicating a first order transition for $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$. We speculate that the recent experimental findings that disorder removes the first order transition are consistent with these calculations.