Coupling between charge-density excitations and polar optical phonons in single quantum wells revisited

We report a detailed analysis of the coupling between the polar longitudinal optical (LO) phonon and intersubband charge-density excitations of a two-dimensional electron gas which forms in three GaAs single quantum wells of different thickness. Inelastic light scattering spectra exhibit different intersubband charge excitations depending on the number of occupied subbands (one or two). The coupling to the LO phonon was tuned by changing the electron density with a gate bias. Calculations of the coupled modes using a dielectric tensor formulated within the local density approximation allowed for a successful peak assignment. Among several striking coupling effects, we were able to identify a statically screened LO phonon mode