Long-Wave Optical Vibrations in Diatomic Ionic Crystals
Keywords:ionic crystal, electromagnetic field, long-wave vibrations, phonon-polaritons, longitudinal optical phonons, harmonics
Long-wave phonon-polaritons and longitudinal optical phonons have been considered as eigen-waves of the electromagnetic field in ionic crystals with two atoms per unit cell. The Kun Huang model is used to describe the sublattices of point charges vibrating with the frequency w0. The dispersion laws for optical vibrations in crystals are generalized, by considering the thermal motion of charges. An additional longitudinal phonon with the frequency 2w0 and two upper phonon-polaritons are found in the second-order approximation with respect to the ratio between the standard deviation and the wavelength.
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