Coherent phonons were observed in ${\mathrm{SrTiO}}_3$ by using ultrafast polarization spectroscopy. The ultrafast dynamics and softening of phonon modes, which contribute to the structural phase transition at $105\mathrm{K}$, are studied. The temperature dependences of the phonon frequency and the relaxation rate are obtained from the observed damped oscillation of coherent phonons. The observed phonon relaxation is explained well by a population decay due to anharmonic phonon-phonon coupling for the soft mode phonons.

• Received 20 March 2006

DOI:https://doi.org/10.1103/PhysRevB.74.064303