THE ORIGIN OF GLASSY DYNAMICS IN THE 2D FACILITATED KINETIC ISING-MODEL

Monte Carlo simulation data from the two-dimensional facilitated kinetic Ising model proposed by Fredrickson and Andersen is examined with the goal of understanding the processes responsible for the characteristic features of glassy dynamics. The spatial distribution of spin flip rates is found to be highly nonuniform with pockets of rapidly relaxing spins surrounded by kinetically locked domains. The slow relaxation of these latter domains, which gives rise to the characteristic long time tail of the linear response function, is due to the action of rare clusters of spins which are able to propagate their influence throughout the sample. An analytic expression is derived for the density of these active sites which is found to fully account for the non-Arrhenius temperature dependence of the relaxation time in this model. The consequences of these results for both theories and experiments in structural glasses are discussed.