Polaronic-type excitons in ferroelectric oxides: Microscopic calculations and experimental manifestation

We discuss the current experimental and theoretical understanding of new polaronic-type excitons in ferroelectric-oxides charge-transfer vibronic excitons ~CTVE’s!, which are pairs of strongly correlated electronic and hole polarons. It is shown that charge-transfer‐lattice distortion interactions are the driving forces for CTVE formation. Hartree-Fock-type calculations performed in the framework of the intermediate neglect of differential overlap ~INDO! method as well as photoluminescence, second-harmonic generation, and UVabsorption high-temperature studies performed for ABO3 ferroelectric oxides strongly support the CTVE existence. Both single CTVE and a phase of strongly correlated CTVE’s in their ferroelectric ground and antiferroelectric excited states are analyzed.