ELECTRON-ELECTRON INTERACTIONS IN 2D ELECTRON GASES - INELASTIC LIGHT-SCATTERING-STUDIES AT HIGH-PRESSURE

We report recent inelastic light scattering measurements of elementary excitations of 2D electron gases produced in modulation-doped single and double quantum well structures. The 2D electron density n obtained from photoluminescence data is continuously tuned by applying hydrost atic pressure. Inelastic light scattering yields detailed information on collective intersubband charge-density (CDE) and spin-density excit ations (SDE) from which the Hartree and exchange terms of the Coulomb interaction are obtained as a function of carrier density. In the very dilute regime (n < 5 x 10(10) cm(-2)) we find that exchange-correlati on effects become more important than the Hartree term of the electron -electron interaction. Further reduction of the electron density with pressure drives the 2D electron gas through a metal-nonmetal transitio n characterized by the collapse of the Hartree term. This transition, however, is suppressed in a double quantum well system due to the enha ncement of screening effects in the interacting bilayer electron gas.