Lane formation in colloidal mixtures driven by an external field.

The influence of an external field on a binary colloidal mixture performing Brownian dynamics in a solvent is investigated by nonequilibrium computer simulations and simple theory. In our model, one half of the particles are pushed into the field direction while the other half of them are pulled into the opposite direction. For increasing field strength, we show that the system undergoes a nonequilibrium phase transition from a disordered state to a state characterized by lane formation parallel to the field direction. The lanes are formed by the same kind of particles moving collectively with the field. Lane formation accelerates particle transport parallel to the field direction but suppresses massively transport perpendicular to the field. We further show that lane formation also occurs in a time-dependent oscillatory field. If the frequency of the external field exceeds a critical value, however, the system exhibits a transition back to the disordered state. Our results can be experimentally verified in binary colloidal suspensions exposed to external fields under nonequilibrium conditions.