Plasmon-phonon-polaritons in p-doped Bi-Sb alloys

The phonon spectra of Bi crystals and Bi-Sb alloys indicate the presence of phonon-polaritons caused by the polarization of valence electrons, which reduces the rigidity of the transverse mode of optical lattice vibrations and increases the rigidity of the longitudinal mode of vibrations. Doping Bi-Sb alloys with Sn (p-type impurity) decreases the difference in the energy of plasma oscillations of free charge carriers and the energy of longitudinal optical phonons. In this case, the behavior of the dielectric function is described in terms of the model corresponding to the excitation of plasmon-phonon-polaritons.