Abstract: Using Landau-Ginsburg-Devonshire theory, we derive and analyze analytical expressions for the frequency dispersion of soft phonon modes in nanosized ferroics and perform numerical calculations for a thin SrTiO3 film. We revealed the pronounced “true” size effect in the dependence of soft phonon spatial dispersion on the film thickness and predict that it can lead to the “apparent” or “false” size effect of dynamic flexoelectric coupling constants. Also, we derived analytical expressions describing the influence of finite size effect on the appearance and properties of the incommensurate spatial modulation induced by the static flexoelectric effect in ferroic thin films. To verify the theoretical predictions experimental measurements of the soft phonon dispersion in nanosized ferroics seem urgent.
Title: Size effect of soft phonon dispersion in nanosized ferroics
DOI: https://doi.org/10.1103/PhysRevB.99.115412 Physical Review B (2019) 99, 115412
Preprint deposited in the repository: http://arxiv.org/abs/1812.04702