Anisotropy of the optical dielectric function in the ab plane for YBa2Cu3O7- delta.

Abstract

We report ellipsometric measurements from surfaces of three single-crystal samples of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. Two of the samples were untwinned with ${\mathit{T}}_{\mathit{c}}$=90 and 66 K. The third sample was a tetragonal single crystal with low oxygen content (\ensuremath{\delta}\ensuremath{\sim}0.9). We used solutions for ${\mathrm{\ensuremath{\varepsilon}}}^{\mathit{c}}$ obtained from measurements on two faces of thick, single-crystal, twinned samples to solve for the other two components of the dielectric tensor (${\mathrm{\ensuremath{\varepsilon}}}^{\mathit{a}}$ and ${\mathrm{\ensuremath{\varepsilon}}}^{\mathit{b}}$). We examine anisotropy in the ab plane and observe unexplained polarization of several peaks, in the middle range of oxygen content. Most notably, we observe a b-polarized feature at 4.16 eV and an a-polarized feature at 4.59 eV for ${\mathit{T}}_{\mathit{c}}$=66 K, which we propose to be a splitting of the 4.03-eV peak observed in the insulator.