Intersubband plasmon excitations of an electron gas in a cylindrical quantum-well wire

A self-consistent energy-functional perturbation theory is presented for an electron gas confined in a quantum-well wire. An analytical expression of the dynamic dielectric function is obtained. It is found that besides the intrasubband mode, when the angular quantization is taken into consideration, intersubband plasmon modes exist in the single-quantum-well-wire structure. These intersubband modes have excitation energies well beyond the single-particle excitation continuum, and they are out of Landau damping. It is resonable to expect that these intersubband plasmons should be observable in experiment.