FAR-INFRARED ABSORPTION IN PARALLEL QUANTUM WIRES WITH WEAK TUNNELING

We study collective and single-particle intersubband excitations in a system of quantum wires coupled via weak tunneling. For an isolated wi re with parabolic confinement, Kohn's theorem guarantees that the abso rption spectrum represents a single sharp peak centered at the frequen cy given by the bare confining potential. We show that the effect of w eak tunneling between two parabolic quantum wires is twofold: (i) addi tional peaks corresponding to single-particle excitations appear in th e absorption spectrum, and (ii) the main absorption peak acquires a de polarization shift. We also show that the interplay between tunneling and weak perpendicular magnetic field drastically enhances the dispers ion of single-particle excitations. The latter leads to a strong dampi ng of the intersubband plasmon for magnetic fields exceeding a critica l value. The results are obtained within a random-phase approximation for the total potential and at low electron concentration, where the s creening effects are treated perturbatively.