ROLE OF PERCOLATION IN-DIFFUSION ON RANDOM LATTICES

Diffusion of single particles on lattices with random distributions of static barriers (random-barrier model) is investigated by Monte Carlo simulations and the time-dependent effective-medium approximation. The crossover from anomalous to linear diffusive behavior is discussed in terms of a percolation model. For a discrete distribution of barrier heights with a small concentration of ''defect'' barriers at the percolation threshold, an alternative kind of transition from bulk-controlled to defect-controlled diffusion is observed as the temperature decreases.