Inelastic light scattering on coupled plasmon-LO phonon modes in high magnetic fields

We report on the results of high-magnetic-held (up to 28T) inelastic light scattering measurements of coupled plasmon-phonon modes in metallic GaAs sa mples with electron concentrations ranging from 10(17) to 2 x 10(18) cm(-3) . The zero-field Raman spectra of the investigated samples show peaks relat ed to the transverse optical phonon (TO) as well as the coupled plasmon-pho non omega (-) (below TO frequency) and omega (+) (above LO frequency) modes . In the backscattering Voigt geometry (k perpendicular to B) in which the modes propagating across the field direction are probed, the magnetic field does not influence the TO resonance but leads to a splitting of both omega (+) and omega (-) branches. The experimental data are approximated using t he dielectric function formalism. For a highly doped sample, the interactio n between coupled plasmon-phonon modes with the Bernstein mode is observed. (C) 2001 Elsevier Science B.V. All rights reserved.