EFFECT OF THE IMAGE POTENTIAL ON PLASMONS IN CYLINDRICAL QUANTUM-WELL WIRES

The collective electronic excitations in quasi-one-dimensional cylindrical quantum-well wires are studied theoretically. Using a two-subband model the dispersion curves of the intra- and intersubband plasmons in the random-phase approximation for the cases of one and two occupied subbands are calculated. The influence of the image forces on the intra- and intersubband plasmon is studied in detail. New explicit analytical expressions for the dispersion relations, valid in a wide range of the wave vector are derived. It is shown that the additional intrasubband plasmon, arising if two subbands are occupied, has for small wave vectors a linear dispersion and is independent of the dielectric screening of the quantum-well wire. The intersubband plasmon is split in two branches, one with a positive and one with a negative dispersion. The electric dipole moment of the collective excitations is calculated and the selection rules for the coupling of light with the plasmons are derived.