Weak localization of disordered quasiparticles in the mixed superconducting state

Starting from a random-matrix model, we construct the low-energy effective-held theory for the noninteracting gas of quasiparticles of a disordered superconductor in the mixed state. The theory is a nonlinear sigma model, with the order-parameter field being a supermatrix whose form is determined solely on symmetry grounds. The weak-localization correction to the field-axis thermal conductivity is computed for a dilute array of s-wave vortices near the lower critical field H-c1. We propose that weak-localization effects, cut off at low temperatures by the Zeeman splitting, are responsible for the field dependence of the thermal conductivity seen in recent high-T-c experiments by Aubin et al. [S0163-1829(99)08205-3].