Exchange and correlation in the nonhomogeneous electron gas in semiconductor heterojunctions

We present a detailed comparison between experiment and theory of the magnitude of the exchange-correlation Coulomb interaction in the collective intersubband spin-density excitation of the electron gas confined to GaAs/AlGaAs quantum wells. A widely used self-consistent-field theory in which exchange and correlation is incorporated through the local-density approximation is found to underestimate slightly the magnitude of the interaction, while a nonlocal theory involving a variational solution of the Bethe-Salpeter equation for the density-density correlation function compares well with experiment.