Observation of coupled cyclotron-plasmonlo phonon modes in InSb for sample configurations ranging from Faraday to Voigt

In an external magnetic field the coupled plasmon-LO phonon modes interact with the single-particle cyclotron modes to produce, in general, three modes which are i.r. active for all sample configurations except the Faraday configuration. In normal-incidence experiments on a thin sample of n-InSb, we have observed the shift in position of the coupled-mode resonance absorption lines as the magnetic field is tilted in steps from the Faraday to the Voigt configuration. We also observed the magnetic field dependence of the intensity and width of the absorption lines which are related to the electron and LO phonon strengths of the modes. Calculations of transmittance and reflectance are in good qualitative agreement with the experimental observations.