Photoinduced Dynamics in Pure and Ca-Doped SrTiO3 Studied by Transient Birefringence and Absorption Measurements

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The photoinduced dynamics of the lattice deformation and the relaxed excited state in SrTiO3 is studied by stationary- and transient-birefringence and pump--probe measurements in comparison with the doping-induced ferroelectric lattice deformation in Ca-doped SrTiO3. Ca-doped SrTiO3 is found to exhibit first-order-like structural deformation with a small threshold UV intensity ({\sim}10^{-3} mW/mm2), and it is also found to exhibit a shift in the ferroelectric transition temperature under UV illumination. The photoinduced lattice deformation has the same order of magnitude as the ferroelectric lattice deformation, and it is not affected by the electric field. The occupation probability in the relaxed excited state is found to increase significantly at low temperatures. These experimental results suggest that the photoinduced giant dielectric response of SrTiO3 is consistent with the conductive-region model rather than the ferroelectric cluster model. SrTiO3 is a peculiar material in which dielectricity of the Maxwell--Wagner type appears in a stoichiometric material only under UV illumination.
2011-10-15