Hybridization and electron-phonon coupling in ferroelectric BaTiO3 probed by resonant inelastic x-ray scattering

We investigated the ferroelectric perovskite material BaTiO3 by resonant inelastic x-ray scattering (RIXS) at the Ti L-3 edge. We observe with decreasing temperature a transfer of spectral weight from the elastic to the charge-transfer spectral features, indicative of increasing Ti 3d-O 2p hybridization. When the incident photon energy selects transitions to the Ti 3d e(g) manifold, the quasielastic RIXS response exhibits a tail indicative of phonon excitations. A fit of the spectral line shape by a theoretical model allows us to estimate the electron-phonon coupling strength M similar to 0.25 eV, which places BaTiO3 in the intermediate coupling regime.