Coupled plasmon-phonon excitations in quasi-one-dimensional quantum-well wires

The spectrum of the coupled plasmon-phonon collective excitations of a quasi-one-dimensional quantum-well wire is analyzed. Using a three-subband model the electronic polarization function is treated in detail within the random-phase approximation. It is found that, in comparison with the quasi-two-dimensional electron gas, the excitation spectrum of the quasi-one-dimensional electron gas contains additional regions free of Landau damping. The dispersion curves of the collective excitations are calculated and presented in graphical form for three different cases of subband population. It is shown that the plasmon-phonon coupling can appreciably shift the dispersion curves. In the case that more than one subband is populated, we have found additional plasmonlike intersubband modes that exist in regions observable in far-infrared optical spectroscopy.