Plasmon–phonon and plasmon–two different phonon interaction in Pb1−xMnxTe mixed crystals

Far-infrared reflection spectra in wide temperature range was used to investigate the vibrational properties of Pb1−xMnxTe (x = 0.0002, 0.002, 0.02 and 0.1) mixed crystals. To analyse the experimental results we use dielectric function that takes into account the existence of plasmon–phonon as well as the plasmon–two different phonon interaction. The best fit method revealed two frequencies of plasmon–phonon coupled modes and three frequencies of plasmon–two different phonon coupled modes. Further, the values for two different LO modes and plasma frequency (ωP) are calculated. Results obtained from experimental spectra as the best fit, are in very good agreement with the theoretical prediction. The model of phonon behaviour based on Genzel's model was developed. It was found that the long wavelength optical phonon modes of these mixed crystals, exhibit an intermediate and two mode behaviour, coincidentally.