Huge broadening of the crystal-fluid interface for sedimenting colloids

For sedimenting colloidal hard spheres, the propagation and broadening of the crystal-fluid interface is studied by Brownian dynamics computer simulations of an initially homogeneous sample. Two different types of interface broadenings are observed: the first occurs during growth and is correlated with the interface velocity, the second is concomitant with the splitting of the crystal-fluid interface into the crystal-amorphous and amorphous-liquid interfaces. The latter width is strongly peaked as a function of the gravitational driving strength with a huge amplitude relative to its equilibrium counterpart.