Evaluation of the electron–TO–phonon interaction in polar crystals from experimental data

The aim of this study was to determine the strengths of the coupling of electrons with the polar long-wavelength transverse optical (TO) vibrations from infrared spectroscopy data. This determination is made by means of a simple relationship between the electron–TO–phonon interaction constant and material parameters, based on a parametrization of the electron–TO–phonon coupling in terms of the long-range dipole–dipole interaction. The combination of experimental data employed here allowed us to calculate directly the relevant constants for a number of representative polar insulators and to show that in ferroelectrics the interband electron–TO–phonon interaction at the ΓΓ point is essentially strong. In these calculations, infrared spectroscopy methods proved to be an effective tool for study of the main properties of electron interaction with polar long-wavelength TO phonons.