  Biased diffusion of two species with conserved dynamics on a 2xL periodic
lattice is studied via Monte Carlo simulations. In contrast to its simple
one-dimensional version on a ring, this quasi one-dimensional model
surprisingly exhibits phase separation in its steady state, which is
characterized by one macroscopic particle cluster. We study the order parameter
and the cluster-size distributions as a function of the system size L, to
support the above picture.
