Uphill currents in coupled, driven zero--range processes.

In particle systems subject to a nonuniform drive, particle migration is observed from the driven to the non-driven region and vice-versa, depending on details of the hopping dynamics, leading to apparent violations of Fick's law and of steady-state thermodynamics. We propose and discuss a very basic model in the framework of the zero-range process, in which this phenomenon is observed and fully explained.