Group Theoretical Selection Rules for Two-Phonon Processes in Rocksalt Type Crystals under Electrostatic Fields

Abstract

Raman and infrared activities and splitting features caused by the perturbations of [0, 0, 1], [1, 1, 1] and [1, 1, 0] electric fields are tabulated. As all of the field-perturbed two-phonon processes are Raman active, splitting features and polarization dependences may be useful for the interpretation of spectra. Most of the infrared inactive two-phonon processes are ralaxed into active. The observation of infrared peaks is expected in high frequency region where few field-free peaks have been observed.