Coupling between Light and Terahertz-Frequency Acoustic Phonons in Ferroelectric BaTiO3/SrTiO3 Superlattices

A. BRUCHHAUSEN, A. FAINSTEIN, S. TINTE, A. SOUKIASSIAN, D. SCHLOM, AND X. X. XI

CHINESE JOURNAL OF PHYSICS

PHYSICAL SOC REPUBLIC CHINA

Lugar: Taipei; Año: 2011 vol. 49 p. 159 - 170

0577-9073

The acoustic phonons in epitaxial ferroelectric (BaTiO(3))(n)/(SrTiO(3))(m) superlattices (SLs) are investigated by high-resolution ultraviolet Raman scattering. The temperature dependence of the folded acoustic (FA) phonon Raman intensity through the ferroelectric transition is addressed. A comparison of this behavior between SLs with different number of ferroelectric BaTiO(3)unit cells n and spacer SrTiO(3) unit cells m is presented. A mechanism involving the strain modulation of the spatially varying ferroelectric polarization is introduced to explain the temperature dependence of the FA phonon scattering. The temperature dependence of the polarization can be derived from an analysis of the first-order optical phonon spectra. Using this information, the observed temperature dependence of the whole set of SLs with different n can be consistently accounted for with the presented model. Atomistic shell-model simulations of the spatial pattern of the SL polarization are presented to explain the variation of the FA-spectral intensity for SLs with different m and the experimental fact that no high-order FA-replicas are observed. These results demonstrate the strong coupling between THz hypersound, charge, and light in these multifunctional nanoscale ferroelectrics.