Non-monotonic crossover from single-file to regular diffusion in micro-channels

The diusion behavior of interacting particles determines the behavior of a large number of systems ranging from pedestrians crossing a road to ions passing through channels in living cells. Here we present a system in which the nature of the diusion process varies with changes in the external conditions. We nd this special behavior in a colloidal model system, consisting of micron sized particles which are conned to narrow channels and interact via induced magnetic dipoles. When the density of these particles is changed, diusion alternates between normal Fickian behavior and single-le diusion. This anomalous behavior is induced by the order of the particles in the restricted geometry and does not depend on the exact nature of the inter-particle interactions.