Double quantum wire plasmon instability

We examine the conditions for current-driven plasma instability in a double quantum wire system. The standard RPA formulation of longitudinal plasmon dispersion is employed to analyze the collective modes of this system in the presence of steady currents, which we consider to be equal and opposite in the two wires. We show that, for wires carrying equal steady currents in opposite directions, the quasi-ID plasma waves propagating along the wires become unstable when the electron drift velocity falls between the phase velocities of the acoustic and optical plasma modes of the Coulomb-coupled wires.