EFFECT OF THE IMAGE POTENTIAL ON PLASMONS IN CYLINDRICAL QUANTUM-WELLWIRES

The collective electronic excitations in quasi-one-dimensional cylindr ical quantum-well wires are studied theoretically. Using a two-subband model the dispersion curves of the intra- and intersubband plasmons i n the random-phase approximation for the cases of one and two occupied subbands are calculated. The influence of the image forces on the int ra- and intersubband plasmon is studied in detail. New explicit analyt ical expressions for the dispersion relations, valid in a wide range o f the wave vector are derived. It is shown that the additional intrasu bband plasmon, arising if two subbands are occupied, has for small wav e vectors a linear dispersion and is independent of the dielectric scr eening 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 a re derived.