Random organization in periodically driven systems

Understanding self-organization is one of the key tasks for controlling and manipulating the structure of materials at the micro- and nanoscale. In general, self-organization is driven by interparticle potentials and is opposed by the chaotic dynamics characteristic of many driven non-equilibrium systems. Here we introduce a new model that shows how the irreversible collisions that generally produce diffusive chaotic dynamics can also cause a system to self-organize to avoid future collisions. This can lead to a self-organized non-fluctuating quiescent state, with a dynamical phase transition separating it from fluctuating diffusing states. We apply the model to recent experiments on periodically sheared particle suspensions where a transition from reversible to irreversible behaviour was observed. New experiments presented here exhibit remarkable agreement with this simple model. More generally, the model and experiments provide new insights into how driven systems can self-organize. Random collisions between particles usually generate disorder in a system. But under certain conditions, particles in suspended in a liquid subjected to periodic shear forces can collide in a way that leads to fewer subsequent collisions and less disorder.