Chaos and anomalous diffusion of adatoms on solid surfaces

The microscopic diffusional dynamics of Na adatoms on a Cu~001! surface is modeled by the classical deterministic motion of a particle from a two-dimensional periodic potential previously fitted to the experiment. Depending on the energy of the particle, a series of chaotic transitions take place determining transport properties of the system. Two different regimes of diffusion, anomalous and normal, are reported and related to the chaotic dynamics. Simple periodic orbits are responsible for frustrated vibrational motions as well as unusual high rate of migration paths along particular directions. The connection between Lévy flights and the principal periodic orbits of the system is established, as well as the validity of some statistical models proposed to describe the anomalous diffusion process. The influence of noise and dissipation on this dynamics is also briefly discussed.