  Solitons are commonly known as waves that propagate without dispersion. Here
we show that they can occur for driven overdamped Brownian dynamics of hard
spheres in periodic potentials at high densities. The solitons manifest
themselves as periodic sequences of different assemblies of particles moving in
the limit of zero noise, where transport of single particles is not possible.
They give rise to particle currents at even low temperature that appear in
band-like structures around certain hard-sphere diameters. At high
temperatures, the band-like structures are washed out by the noise, but the
particle transport is still dominated by the solitons. All these predicted
features should occur in a broad class of periodic systems and are amenable to
experimental tests.
