  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.
