PERSISTENT CURRENTS IN AN ENSEMBLE OF ISOLATED, MESOSCOPIC RINGS AT ZERO TEMPERATURE - A NONPERTURBATIVE APPROACH

Using the supersymmetry method we present a nonperturbative calculation of the ensemble-averaged persistent current at zero temperature. Special care is taken to exactly restrict the particle number on each ring to an integer value. Our result is obtained by integrating exactly over a Goldstone mode of zero momentum in a domain of flux values where perturbation theory fails. Thus we extend previous perturbative calculations to the vicinity of half-integer multiples of the magnetic-flux quantum, a regime inaccessible up to now at zero temperature.