OPTICAL-PROPERTIES OF THE Y-BA CUPRATES - MAINLY A BAND-STRUCTURE POINT-OF-VIEW

Using rotating analyser ellipsometry we have determined the dielectric tensor of the superconducting Y-Ba cuprates and their relatives in the energy range between 700 meV and 23 eV. We have also performed ab initio calculations of the optical response, based on a linear muffin tin orbital band structure. Experimental and theoretical spectra agree beautifully. The comparison of experiment and theory allows us to assign the peaks to critical points in the Brillouin zone. Independent tests for our assignments are constructed by monitoring the change in the optical properties induced by varying the oxygen stoichiometry, replacing Y by Pr or introducing oxygen disorder. All these experiments yield results compatible with our assignments. Besides answering fundamental questions about the validity of the band structure approach and the microscopic origin of the optical properties of these materials, the data may also play a useful role in the optical characterization of materials.