ANOMALOUS DIFFUSION DUE TO OBSTACLES - A MONTE-CARLO STUDY

In normal lateral diffusion, the mean-square displacement of the diffu sing species is proportional to time. But in disordered systems anomal ous diffusion may occur, in which the mean-square displacement is prop ortional to some other power of time. In the presence of moderate conc entrations of obstacles, diffusion is anomalous over short distances a nd normal over long distances. Monte Carlo calculations are used to ch aracterize anomalous diffusion for obstacle concentrations between zer o and the percolation threshold. As the obstacle concentration approac hes the percolation threshold, diffusion becomes more anomalous over l onger distances; the anomalous diffusion exponent and the crossover le ngth both increase. The crossover length and time show whether anomalo us diffusion can be observed in a,given experiment.