Optical response of oxide dielectrics

The optical response of oxide dielectrics is calculated by using a combination of self-consistent phonon theory together with results obtained from exactly solving a nonlinear electron-phonon interaction model in the continuum limit. The model is based on the unusual oxygen ion polarizability which induces multiphonon density-density interactions. The damping of optic modes together with an increase in oscillator strength and the development of line shape anomalies with decreasing temperature, is obtained in agreement with experimental data. Unusual mass dependences of optic modes are observed, and the origin of the damping of these phonon modes is identified. The results may provide a fundamental understanding of sum rule violations observed in many dielectrics.