Monitoring of Longitudinal-Wave Velocity and Attenuation of SrTiO_3 at Low Temperatures Using Picosecond Ultrasound Spectroscopy

摘要

We measured the longitudinal-wave velocity and its attenuation in SrTiO_3 between 20 and 300 K using picosecond ultrasound spectroscopy. From the temperature dependence of the velocity and attenuation, we monitored the cubic-tetragonal phase transition of SrTiO_3 near 100 K, whereas no more transitions were indicated below 100 K. From the measured attenuation coefficients, we estimate the relaxation time r. Because of the ultrahigh frequency measurements, the product cot is larger than unity, where the traditional theory for phonon-phonon interaction fails to explain the relaxation time. We then derived the relationship between the relaxation time and attenuation for ωt >1.