Stripes, Clusters, and Nonequilibrium Ordering for Bidisperse Colloids   with Repulsive Interactions
  We show that two-dimensional bidisperse assemblies of colloids with strictly repulsive interactions exhibit stripe, cluster, and partially crystallized states when driven over a quenched random substrate. The nonequilibrium states on a substrate are significantly more ordered than equilibrium states both with and without substrates. A minimum substrate strength is necessary to induce the nonequilibrium pattern formation. Our results suggest that a combination of driving and quenched disorder offers a new approach to controlling pattern formation in colloid mixtures. 
C. Reichhardt and C.J. Olson Reichhardt