Nonuniversal correlations and crossover effects in the Bragg-glass phase of impure superconductors

The structural correlation functions of a weakly disordered Abrikosov lattice are calculated in a functional RG expansion in d = 4 - epsilon dimensions. It is shown that in the asymptotic limit the Abrikosov lattice exhibits still quasi-long-range translational order described by a nonuniversal exponent eta (G) which depends on the ratio of the renormalized elastic constants kappa = c(66)/c(11) of the flux line (FL) lattice. Our calculations clearly demonstrate three distinct scaling regimes corresponding to the Larkin, the random manifold, and the asymptotic Bragg-glass regime. On a wide range of intermediate length scales the FL displacement correlation function increases as a power law with twice the manifold roughness exponent zeta (RM)(kappa), which is also nonuniversal. Correlation functions in the asymptotic regime are calculated in their full anisotropic dependencies and various order parameters are examined. Our results, in particular the kappa dependency of the exponents, are in variance with those of the variational treatment with replica symmetry breaking which allows in principle an experimental discrimination between the two approaches.