Researchers: Leonel Perondi, Sir Roger Elliott*, and Kimmo Kaski
*Oxford University, UK
There has been a considerable interest in the development of new techniques for treating microscopic diffusion phenomena in ordered as well as disordered many-particle systems. As is well known many-particle effects may play a key role on the diffusion-related properties of a system. Applications range from ionic conduction in electronic insulators (ionic conductors) to electronic transport in semiconductors.
An isolated particle in contact with a heat reservoir undergoes a random walk montion (brownian motion), which may be characterized by a linear relation between the mean square displacement and time. The linear coefficient gives the free-particle diffusion constant D0. In an interacting many-particle system, the single-particle (tracer) diffusion constant is changed to fb fc D0, where fb and fc are termed the blocking and correlation factors, respectively. The blocking factor is a measure of the probability of a successful single-particle hop. Since the presence of other particles tends to hinder the movement of any given particle, fb is less than one. The correlation factor arises from the fact that interactions produce correlation among successive displacements. Such correlations slow down the diffusion process and fc is also less than one. The presence of static defects in the space in which the diffusion process takes place, further enhances both effects. Depending on the nature and concentration of such defects new diffusive regimes may settle in. In particular, when the mean square displacement increases with time to some power less than one, the diffusive regime is called anomalous.
One of the main objectives of the present project is the study of diffusion in many-particle systems in which the blocking and correlation effects may lead to an anomalous diffusive behaviour.