Anisotropic thermally activated diffusion in percolation systems.

We present a study of static and frequency-dependent diffusion with anisotropic thermally activated transition rates in a two-dimensional bond percolation system. The approach accounts for temperature effects on diffusion coefficients in disordered anisotropic systems. Static diffusion shows an Arrhenius behavior for low temperatures with an activation energy given by the highest energy barrier of the system. From the frequency-dependent diffusion coefficients, we calculate a characteristic frequency omega(c) approximately 1/t(c), related to the time t(c) needed to overcome a characteristic barrier. We find that omega(c) follows an Arrhenius behavior with different activation energies in each direction.