We study transport in the domain state, the so-called zero-resistance state,
that emerges in a two-dimensional electron system in which the combined action
of microwave radiation and magnetic field produces a negative absolute
conductivity. We show that the voltage-biased system has a rich phase diagram
in the system size and voltage plane, with second- and first-order transitions
between the domain and homogeneous states for small and large voltages,
respectively. We find the residual negative dissipative resistance in the
stable domain state.Comment: 5 pages, 4 figure
