Angle-resolved Raman spectroscopy of the collective modes in an electron bilayer

Electronic Raman scattering from GaAs/AlxGa1-xAs double quantum well struct ures has been used to observe the acoustic and optic plasmon modes of an el ectron bilayer system. Angle-resolved measurements allowed direct determina tion of their dispersions for several separations of the electron layers; t hese were well described by corresponding dispersion calculations in the ra ndom-phase approximation (RPA). Qualitative agreement was obtained between measurements of the relative intensities of the acoustic and optic modes an d calculations using a simple nonresonant RPA formalism for the Raman scatt ering cross section. The markedly different linewidths observed for the aco ustic and optic modes are interpreted in terms of the greater localization of the electric fields of the acoustic plasmon, which is therefore much les s susceptible to impurity damping than is the optic plasmon. [S0163-1829(99 ) 14703-9].