Invited
Hyperuniformity in driven suspensions of asymmetric particles

An arrangement of particles is said to be "hyperuniform" if its density fluctuations over large distances are strongly suppressed relative to a random configuration. Crystals, for example, are hyperuniform. Recently, several disordered materials have been found to be hyperuniform. Examples are sheared suspensions and emulsions, and random close packings of hard spheres. We show that externally driven asymmetric particles in a liquid suspension (as in sedimentation, for example) self-organize hyperuniformly. This dynamic phenomenon arises from the long-range coupling, induced by the force and carried by the fluid, between the concentration of particles and their velocity. For certain particle shapes the coupling can lead to the opposite effect -- enhancement of density fluctuations and instability. We confirm these analytical results in a simple two-dimensional simulation.