We report a UV-Raman study of folded acoustic vibrations in epitaxial ferroelectric ${\mathrm{BaTiO}}_3/{\mathrm{SrTiO}}_3$ superlattices. The folded acoustic doublets show an anomalous temperature dependence disappearing above the ferroelectric transition, which is tuned by varying the thickness of the ${\mathrm{BaTiO}}_3$ and ${\mathrm{SrTiO}}_3$ layers. A mechanism involving the acoustic phonon modulation of the spatially periodic ferroelectric polarization explains the observed temperature dependence. These results demonstrate the strong coupling between sound, charge, and light in these multifunctional nanoscale ferroelectrics.

• Received 26 December 2007

DOI:https://doi.org/10.1103/PhysRevLett.101.197402