Terahertz dielectric response of cubic BaTiO(3)

A first-principles-based approach is developed to study the dielectric response of paraelectric BaTiO(3), as a function of frequency and temperature. Two different overdamped modes of comparable strengths are found to contribute to such response, in the similar or equal to 1-150 cm(-1) frequency range for temperatures up to similar or equal to 750 K. The lower frequency mode softens toward the Curie point, while the higher-frequency mode stays in the 60-100 cm(-1) range and is associated with temperature-independent short-range correlations. Our far-infrared reflectivity measurements confirm the existence of these two modes, and yield a very good agreement with calculations.