HOLE MAGNETOPLASMONS IN QUANTUM DOTS

For electrons in quantum dots the dipole absorption spectrum is known to reflect only magnetoplasmon modes with a rigid center-of-mass motio n (''generalized Kohn's theorem''). A more complex behavior is expecte d for holes in quantum dots, as the valence-band mixing prohibits the separation of relative and center-of-mass coordinates, and the dipole field couples then also to the relative motion. We investigate theoret ically the far-infrared response of hole-confining quantum dots, assum ing a structure that can be realized by the lateral modulation of a tw o-dimensional hole gas in a GaxAl1-xAs-GaAs quantum well or heterojunc tion. The ground state of the many-hole system is determined in the lo cal density approximation, using the 4x4 Luttinger Hamiltonian to incl ude the valence-band mixing. The collective response to a dipole field is calculated within the random phase approximation. The resulting fa r-infrared absorption spectra exhibit a rich set of dipole active magn etoplasmon modes with internal motions of the charge density, which du e to the generalized Kohn's theorem are not possible for electrons in quantum dots.