  The Gaussian Effective Potential in a fixed transverse unitarity gauge is
studied for the static three-dimensional U(1) scalar electrodynamics
(Ginzburg-Landau phenomenological theory of superconductivity). In the
broken-symmetry phase the mass of the electromagnetic field (inverse
penetration depth) and the mass of the scalar field (inverse correlation
length) are both determined by solution of the coupled variational equations.
At variance with previous calculations, the choice of a fixed unitarity gauge
prevents from the occurrence of any unphysical degree of freedom. The theory
provides a nice interpolation of the experimental data when approaching the
critical region, where the standard mean-field method is doomed to failure.
