Abstract
The anisotropic optical properties of multiferroic thin films have been determined with Mueller matrix ellipsometry at room temperature. The full dielectric tensors of tetragonal-like and rhombohedral-like phases epitaxially grown on and single crystal substrates, respectively, within the spectral range of 0.6 and 6.5 eV are reported. Strain-driven anisotropy changes and transition shifts are observed as well as evidence of sub-band gap many-particle excitations are found. The transition shifts, mostly to higher energies for the highly strained tetragonal-like phase on , are indicative of band structure differences. Additionally, optical modeling, confirmed by piezoelectric force microscopy studies, revealed that the average polarization direction of bivariant on is not parallel to the crystallographic [001] direction but tilted by about . Spectral weight analyses reveal phase-dependent differences, underlining that theoretical calculations of optical spectra need further improvement to appropriately account for electronic and excitonic correlations to fully understand multiferroic .
- Received 27 July 2015
- Revised 12 August 2015
DOI:https://doi.org/10.1103/PhysRevB.92.075310
©2015 American Physical Society