Anomalous behaviour of the diffusion coefficient in interacting adsorbates

Langevin simulations provide an effective way to study collective effects of Brownian particles immersed in a two-dimensional periodic potential. In this paper, we concentrate essentially on the behaviour of the tracer (DTr) and collective diffusion coefficients (DC) as function of friction (Γ). Our simulations show that in the high friction limit, the two physical quantities DTr and DC present qualitatively the same behaviour, for both coupled and decoupled substrate potentials. However, for the low friction regime, and especially for the coupled potential case, an anomalous diffusion behaviour is found where DTr∼Γ-σTr and DC∼Γ-σC, with σTr<σC<1. We also found that in the case of weak dynamical coupling between the adparticles and the substrate, the exponents are not universal and rather depend on the potentials. Moreover, changes in the inter-particle potentials may reverse the behaviour to a normal one.