Observation of TO1 soft mode in SrTiO3 films by terahertz time domain spectroscopy

Abstract

We have measured the dielectric properties of pulsed-laser-deposited SrTiO3 (STO) thin films by terahertz (THz) time-domain spectroscopy in the frequency range from 80GHzto1.5THz at temperatures from 20to290K. The measured frequency dispersion of the dielectric constant of the STO thin films show a clear Lorentzian oscillator behavior below 180K and softening of the ferroelectric soft mode of the STO thin films takes place with decreasing temperature. Both eigen frequency and damping of the soft phonon mode show a peak nearly at 110K that can be attributed to the effect on the Ti–O–Ti bending in STO thin film due to the starting of tilting in oxygen octahedra near the cubic to tetragonal phase transition. Dielectric strength saturates near the temperature 60K, however, that is a point of further investigation.