Evidence for zero-differential resistance states in electronic bilayers
  We observe zero-differential resistance states at low temperatures and moderate direct currents in a bilayer electron system formed by a wide quantum well. Several regions of vanishing resistance evolve from the inverted peaks of magneto-intersubband oscillations as the current increases. The experiment, supported by a theoretical analysis, suggests that the origin of this phenomenon is based on instability of homogeneous current flow under conditions of negative differential resistivity which leads to formation of current domains in our sample, similar to the case of single-layer systems. 
G. M. Gusev, S. Wiedmann, O. E. Raichev, A. K. Bakarov, and J. C.   Portal
cond-mat.mes-hall