Coupled plasmon-LO-phonon modes at high-magnetic fields

High-magnetic-field (up to 28 T) inelastic light scattering experiments on coupled plasmon-LO-phonon modes in degenerate n-type GaAs are reported. The data are analyzed using a standard, dielectric function approach. Results obtained for samples with high electron concentration are well understood. A strong interaction of coupled LO-phonon-plasmon modes with the collective cyclotron resonance excitations (Bernstein modes) is observed. In samples with lower electron concentration, an unexpected Raman scattering signal in the vicinity of the undressed optical phonon is observed at high magnetic fields. A field induced metal-insulator transition is shown to be traced with Raman scattering experiments in samples with the lowest electron concentration.