  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.
