INTERSUBBAND ELEMENTARY EXCITATIONS OF QUASI-2-DIMENSIONAL ELECTRON-SYSTEMS IN QUANTUM-WELL

Theoretical study is made for the dispersion relation and for the spec tra of intersubband elementary excitations in the quasi-two dimensiona l electron gas of GaAs/AlGaAs quantum well. Density-density correlatio n functions appearing in expressions for transition probabilities are calculated by means of the perturbation expansion with respect to the Coulomb interactions between electrons in the conduction subbands. Fro m the calculated results, at long-wavelength limit the effects of the attractive Coulomb interactions between electrons and holes on the ene rgy shift of the collective excitations from the single-particle excit ations are shown to be comparable to the depolarization effects. The p eak positions of the collective charge- and spin-density excitations i n spectra are in qualitative agreement with the recent experimental fi ndings.