Materials that approach a ferroelectric transition, where they acquire spontaneous electric polarization, typically exhibit a softening of an eigenmode of the lattice vibrations. This implies that atoms can move with less force in the direction of their position in the ferroelectric phase. A well-known example of such behaviour is observed in SrTiO3, where the transition does not occur when lowering the temperature due to quantum fluctuations.
In our study, we employed inelastic neutron scattering at the Spallation Neutron Source SINQ at the Paul Scherrer Institute to investigate the effects of applying a significant electric field to SrTiO3. We focused on the dynamics of the dispersion of collective behaviour of the soft mode, a topic that has surprisingly not been thoroughly explored before. Our findings indicate that the electric field causes a stiffening of the soft mode, though the overall dispersion characteristics are not significantly altered. The stiffening suggests that the applied electric field increases the effective binding of atoms along its direction. Moreover, we also observed that the mode perpendicular to the applied force is also affected, albeit to a lesser, implying a coupling of the modes. Additionally, we identified a coupling to the acoustic mode that the lattice dynamics of this prototypical materials continue to offer valuable insights, even after decades of research.
Contact
Dr. Urs Staub
PSI Center for Photon Science
+41 56 310 4494
urs.staub@psi.ch
Original Publication
Phonon dispersion of quantum paraelectric SrTiO3 in electric fields
Henrik Jacobsen, Marek Barthkowiak, Tobias Weber, Uwe Stuhr, Bertrand Roessli, Christof Niedermayer and Urs Staub
Phys. Rev. B110, 054302 (2024), https://doi.org/10.1103/PhysRevB.110.054302 (link is external)