Condensation transitions in a two-species zero-range process

We study condensation transitions in the steady state of a zero-range process with two species of particles. The steady state is exactly soluble-it is given by a factorized form provided the dynamics satisfy certain constraints-and we exploit this to derive the phase diagram for a quite general choice of dynamics. This phase diagram contains a variety of mechanisms of condensate formation, and a phase in which the condensate of one of the particle species is sustained by a "weak" condensate of particles of the other species. We also demonstrate how a single particle of one of the species (which plays the role of a defect particle) can induce Bose condensation above a critical density of particles of the other species.