Barium titanate (BaTiO₃), a classic ferroelectric, shows a coupling between light, electrons and phonons that depends strongly on crystallographic direction, according to a study combining ultrafast spectroscopy with carrier dynamics analysis. The observed anisotropy in the relaxation of photo-induced carriers suggests that the material's response to optical excitation is not uniform, but is governed by the orientation of the ferroelectric polarization vector relative to the electric field of the incident light.

The work addresses an open question in the physics of ferroelectric oxides: how the energy deposited by a light pulse is shared between excited electrons, the crystal lattice and the intrinsic piezoelectric coupling of the material. In ferroelectrics such as BaTiO₃, spontaneous polarization introduces a privileged direction in the crystal, but until now direct measurement of how that direction modulates energy transfer between electronic and vibrational subsystems has been scarce.

The method is based on exciting the material with ultrashort optical pulses and tracking the time evolution of the differential reflectance or transmittance, resolved as a function of the crystal orientation of the sample. The observed carrier separation occurs on the scale of hundreds of femtoseconds after excitation, and the comparison between configurations parallel and perpendicular to the polarization allows the electronic contributions to be disentangled from the phononic ones.

The relevance of the result is twofold. On the one hand, it provides a quantitative picture of how the symmetry broken by ferroelectric polarization controls carrier dynamics, useful for the design of optoelectronic and photovoltaic devices based on oxides. On the other hand, it opens the door to strategies for the coherent control of charge separation through the engineering of ferroelectric domain orientation, a field that connects condensed matter physics with energy conversion applications.