Diffusion in a strongly correlated anisotropic overlayer

We study the collective diffusion in chain structures on anisotropic substrates like (1 1 2) bcc and (1 1 0) fcc surfaces with deep troughs in the substrate potential corrugation. These chain structures are aligned normal to the troughs and can move only along the troughs. In a combination of theoretical arguments and of numerical simulations, we study the mass transport in these anisotropic systems. We find that a mechanism similar to soliton diffusion, instead of single particle diffusion, is still effective at temperatures well above the melting temperature of the ordered chain structures. This mechanism is directly correlated with the ordered phases that appear at much lower temperatures. As a consequence, also the influence of frozen disorder is still visible above the melting temperature. Theoretically we predict a strong dependence of the pre-exponential factor and weak dependence of the activation energy on the concentration of frozen surface defects. These predictions are confirmed by the simulations.