Terahertz electromagnetic wave amplification by lateral double-quantum-wire superlattice subject current-driven plasmon instability

The electrodynamic interaction of an incident terahertz electromagnetic wave with a current-carrying lateral double-quantum-wire superlattice is analyzed here. The superlattice (in the x-y plane) is assumed to consist of two parallel quantum-wire sublattices, each of period a, shifted with respect to each other by distance d in the transverse y-direction. The parallel quantum wires of the sublattices are oriented in the x-direction. The two sublattices are taken to carry equal steady currents in opposite directions, and are coupled by Coulomb forces alone, with tunneling neglected. We recently showed that quasi-ID plasmons of such double-quantum-wire superlattice systems become unstable when the electron drift velocity falls between the phase velocities of the acoustic and optical plasma modes of the Coulomb-coupled wire subsystems. Here, a standard RPA formulation of plasmon dispersion taken jointly with the full system of Maxwell equations is employed to describe the electrodynamic interaction of incident terahertz electromagnetic radiation with the superlattice electron system at the plasmon resonant frequencies. Coupling of the electromagnetic wave with plasmon excitations is provided by introducing a metal grating with the grating stripes oriented perpendicular to the quantum wires. We have determined the transmission, absorption and reflection coefficients for an incident terahertz electromagnetic wave propagating through the grating-superlattice system, demonstrating that amplification of the terahertz electromagnetic radiation occurs in the region of plasma instability. Numerical estimates made for GaAs-based structures show that this effect occurs at experimentally achievable drift velocities.