Collective electronic excitations in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells

We report calculations of intersubband spin- and charge-density excitations in quantum wells, using a nonlocal response formalism developed by us in earlier investigations of collective excitations in quantum-confined electron gases. Dispersion curves for these excitations are symmetrically displaced with respect to the single-particle continuum, indicating that direct Coulomb and exchange-correlation interactions have comparable strengths in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As single-well heterostructures. The calculated results, which are based on the local-spin-density approximation for exchange and correlation, are in good agreement with inelastic-light-scattering experiments.