Wave fronts may move upstream in semiconductor superlattices

In weakly coupled, current biased, doped semiconductor superlattices. domai n walls may move upstream against the flow of electrons. For appropriate do ping values, a domain wall separating two electric-field domains moves down stream below a first critical current, it remains stationary between this v alue and a second critical current, and then moves upstream above. These co nclusions are reached by using a comparison principle to analyze a discrete drift-diffusion model, and validated by numerical simulations. Possible ex perimental realizations are suggested.