Photo-induced suppression of ferroelectric transition in oxygen-isotope-exchanged SrTiO3

We have investigated photo-induced effects in SrTi(16O1−x18Ox)3, which undergoes a ferroelectric transition at low temperatures. The ferroelectric transition temperature is lowered by inter-band excitation with ultraviolet light due to the screening of the Coulomb interaction by photo-induced carriers. Considering a microscopic mechanism, we concluded that the critical temperature shift is explained by the hardening of the TO mode with the screening effect. It is suggested that some dipoles with a nanometric size exist in 18O-isotope-exchanged SrTiO3(STO18) and the cooperative interactions among them bring about ferroelectric ordering.