Infrared studies of ab-plane oriented oxide superconductors

New results covering a wide frequency and temperature range are presented for the infrared properties of YBa2Cu3O7-δ for light polarized in the ab plane. The normal-state optical conductivity can be described by two processes: a low-frequency Drude absorption that tracks the temperature dependence of the dc conductivity and a temperature-independent midinfrared band. In the superconducting state most of the oscillator strength of the Drude absorption moves to zero frequency and the reflectance spectrum is dominated by a plasma edge at 500 cm-1. A superconducting gap cannot be seen in our spectra.