The microscopic diffusional dynamics of Na adatoms on a Cu(001) surface were modeled in terms of the classical deterministic motion of a particle from a 2-dimensional periodic potential previously fitted to the experimental data. Depending upon the energy of the particle, a series of chaotic transitions took place which determined the transport properties of the system. Two different regimes of diffusion (anomalous and normal) were reported and were related to the chaotic dynamics. Simple periodic orbits were found to be responsible for frustrated vibrational motions as well as for an unusually high rate of migration along particular directions. A connection between Lévy flights and the principal periodic orbits of the system was established, as well as the validity of some statistical models which had been proposed in order to describe the anomalous diffusion process.

Chaos and Anomalous Diffusion of Adatoms on Solid Surfaces. R.Guantes, J.L.Vega, S.Miret-Artés: Physical Review B, 2001, 64[24], 245415 (11pp)