Oxygen-deficiency-induced localized optical excitations inYBa2Cu3Ox

Abstract

We report two strong electronic transitions in the visible-near-uv optical spectra of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_x$ that are activated by oxygen deficiency. A sharp 4.1-eV excitation is associated with ${\mathrm{Cu}}^{1+}$ and identified with the existence of a highly localized O-Cu(1)-O complex. A second excitation is observed at 1.7 eV when oxygen deficiency or Co substitution makes the material nonsuperconducting. These results emphasize the importance of specific localization and correlation effects in the oxygen dependence of the electronic structure in this compound.