  We consider the unidirectional particle transport in a suspension of
colloidal particles which interact with each other via a pair potential having
a hard-core repulsion plus an attractive tail. The colloids are confined within
a long narrow channel and are driven along by a DC or an AC external potential.
In addition, the walls of the channel interact with the particles via a
ratchet-like periodic potential. We use dynamical density functional theory to
compute the average particle current. In the case of DC drive, we show that as
the attraction strength between the colloids is increased beyond a critical
value, the stationary density distribution of the particles loses its stability
leading to depinning and a time dependent density profile. Attraction induced
symmetry breaking gives rise to the coexistence of stable stationary density
profiles with different spatial periods and time-periodic density profiles,
each characterized by different values for the particle current.
