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

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

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 (BaTiO3 )n /(SrTiO3 )m superlattices (SLs)are investigated by high-resolution ultraviolet Raman scattering. The temperature depen-dence of the folded acoustic (FA) phonon Raman intensity through the ferroelectric transitionis addressed. A comparison of this behavior between SLs with different number of ferroelectric BaTiO3 unit cells n and spacer SrTiO3 unit cells m is presented. A mechanism involvingthe strain modulation of the spatially varying ferroelectric polarization is introduced toexplain the temperature dependence of the FA phonon scattering. The temperature depen-dence of the polarization can be derived from an analysis of the first-order optical phononspectra. Using this information, the observed temperature dependence of the whole set ofSLs with different n can be consistently accounted for with the presented model. Atomisticshell-model simulations of the spatial pattern of the SL polarization are presented to explainthe variation of the FA-spectral intensity for SLs with different m and the experimental factthat no high-order FA-replicas are observed. These results demonstrate the strong couplingbetween THz hypersound, charge, and light in these multifunctional nanoscale ferroelectrics.