INELASTIC LIGHT-SCATTERING STUDY OF MAGNETOPLASMA MODES IN A WIDE PARABOLIC QUANTUM-WELL

Inelastic light scattering was used to study the dispersion and magnet ic-field dependence of both inter-Landau and intersubband magnetoplasm a modes in a wide parabolic quantum well. The intersubband magnetoplas mon energy (approximately 11 meV) was found to be much greater than ex pected from a simple self-consistent Hartree calculation (approximatel y 2 meV). The value is in fact very close to the bare harmonic energy of the well. This striking example of the absence of corrections to th e single-particle energy from electron-electron interactions is the re sult of Kohn's theorem. In a magnetic field, the intersubband magnetop lasmon energy is constant except at the field where the inter-Landau e nergy crosses the intersubband energy. After the crossover, the inters ubband energy shifts to a lower value. This is interpreted as a shift in oscillator strength from a bulklike to a surfacelike magnetoplasma mode.