Electron correlations in an electron bilayer at finite temperature: Landau damping of the acoustic plasmon

We report angle-resolved Raman scattering observations of tie temperature-dependent Landau damping of the acoustic plasmon in an electron bilayer system realized in a GaAs double-quantum-well structure. Corresponding calculations of the charge-density excitation spectrum of the electron bilayer using forms of the random-phase approximation (RPA), and the static local held formalism of Singwi, Tosi, Land and Sjolander (STLS) extended to incorporate non-zero electron temperature T-e and phenomenological damping, are also presented. The STLS calculations include details of the temperature dependence of the intra- and inter-layer local field factors and pair correlation functions. Good agreement between experiment and the various theories is obtained for the acoustic plasmon energy and damping for T-e less than or similar to T-F/2, where T-F is the Fermi temperature. However, contrary to current expectations, all of the calculations show significant departures from our experimental data for T-e greater than or similar to T-F/2. From this, we go on to demonstrate unambiguously that real local field factors fail to provide a physically accurate description of exchange correlation behaviour in low-dimensional electron gases. Our results suggest instead that one must resort to a dynamical local field theory, characterized by a complex field factor to provide a more accurate description.