CRITICAL FIELDS AND CURRENTS IN A WEAKLY NONLINEAR MEDIUM NEAR THE PERCOLATION-THRESHOLD

For fields above a critical value the expansion of the conductivity in powers of the field ceases to be valid and the weak-nonlinearity appr oximation no longer works. The density behavior of the critical fields in strongly inhomogeneous media near the percolation threshold is fou nd on the basis of two criteria-an average criterion and a local crite rion. The parameter values of the medium for which crossover-a change of the critical behavior-occurs are determined. Similar calculations a re performed for the critical currents. (C) 1998 American Institute of Physics. [S1063-7842(98)00206-2].