Frequency- and spin-dependent absorption of surface-acoustic-waves by a 2D electron gas in the quantum Hall regime

The dynamic conductivity of a quasi-two-dimensional electron system with a large spin splitting in high magnetic fields is probed via the acousto-electric interaction with a surface acoustic wave. We compare this interaction for the case of non-spin polarized even and spin polarized odd Landau niveaus of the electron system in the integer quantum Hall regime and find a clear violation of a simple relaxation model that describes other features of the interaction properly. We propose differences in the electrical screening in the quasi-two-dimensional electron system in the case of spin polarized and non-spin polarized Landau levels to explain our experimental findings. (C) 1999 Elsevier Science B.V. All rights reserved.