Soft-mode Dynamics in the Ferroelectric Phase Transition of Quantum Paraelectric SrTiO_3

摘要

The light scattering spectra of the lowest frequency polar mode in the oxygen-isotope induced ferroelectric SrTi~(18)O_3 were observed in both paraelectric and ferroelectric phases. A perfect softening of the E_u mode at the phase transition is observed by the high-resolution spectroscopy in terms of the Fabry-Perot interferometry. The Raman-inactive polar modes are activated by the local symmetry breaking in the centrosymmeiric tetragonal-paraelectric phase. The phase transition mechanism is a perfect displacive type in agreement with the theoretical studies. Both of the perfect softening and the dynamic inhomogeneity enhanced near the critical concentration play an essential role in the oxygen-isotope induced phase transition of SrTi~(18)O_3.