Calculation of plasmonic dispersion in quantum wires: angular degeneracy and shape-confinement effects

We present a random-phase approximation calculation of the collective plasm on excitation spectrum of a one-dimensional electron gas confined in cylind rical and rectangular semiconductor quantum wires. The plasmon spectrum for the cylindrical case is calculated considering up to three occupied subban ds. Taking into account the twofold angular degeneracy of the single-partic le energy spectrum, we derive different expressions for the electron-electr on interaction when opposite angular quantum numbers are involved. That occ urrence leads, even in a two-subband system, to the presence of new undampe d plasmon modes for q --> 0 not exhibited in previous work. Comparing plasm on modes between cylindrical and rectangular quantum wires, we find an inve stigable shape-confinement effect for the intrasubband plasma excitation in the lowest subband.