  For the first time, the dielectric response of a BaTiO3 thin film under an AC
electric field is investigated using time-resolved X-ray absorption
spectroscopy at the Ti K-edge to clarify correlated contributions of each
constituent atom on the electronic states. Intensities of the pre-edge eg peak
and shoulder structure just below the main edge increase with an increase in
the amplitude of the applied electric field, whereas that of the main peak
decreases in an opposite manner. Based on the multiple scattering theory, the
increase and decrease of the eg and main peaks are simulated for different Ti
off-center displacements. Our results indicate that these spectral features
reflect the inter- and intra-atomic hybridization of Ti 3d with O 2p and Ti 4p,
respectively. In contrast, the shoulder structure is not affected by changes in
the Ti off-center displacement but is susceptible to the effect of the corner
site Ba ions. This is the first experimental verification of the dynamic
electronic contribution of Ba to polarization reversal.
