The dielectric tensor elements of oriented YBa2Cu3O7-δ samples, as obtained by spectroscopic ellipsometry, are presented for several oxygen stoichiometries in the photon energy range between 1.66 and 5.5 eV. For δ=0 and 1, we extend this range up to 9.5 eV using a recently developed synchrotron radiation ellipsometer. We compare the experimental results with computed values for the dielectric function obtained from a linear-muffin-tin- orbitals band-structure calculation. We find good general agreement for both the orientational and compositional dependence. In particular, both experiment and theory show c polarization for a peak near 2.7 eV for δ<0.5, while a transition in that spectral region is a polarized for YBa2Cu3O6. In spite of the difficulty in predicting insulating behavior of the low-oxygen material, these results show that the local-density-approximation picture is successful in describing much of the electronic structure determining higher-energy excitations. In addition, the measured dependence of the dielectric tensor on the oxygen stoiochiometry provides a reference for optical determination of the oxygen content and orientation in applications, such as thin-film or single-crystal growth.
ASJC Scopus subject areas
- Condensed Matter Physics