Coherent phonon relaxation in strontium titanate

Ultrafast decays of the intrinsic phonon modes within 260–790 cm−1 range of frequencies, which are symmetry forbidden in the first-order Raman scattering in bulk SrTiO3 crystal, have been traced using time-resolved coherent Raman technique. The effective phonon decay times are within 0.86–1.38 ps and yield corresponding linewidths of 7.7–12.3 cm−1 for optical lattice vibrations. Symmetry breakage mechanisms related to free charged carriers resulting from vacancies do not appear to play a major role.