  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.
