Infrared studies of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>ab</mml:mi></mml:math>-plane oriented oxide superconductors

New results covering a wide frequency and temperature range are presented for the infrared properties of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ for light polarized in the $\mathrm{ab}$ 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 ${\mathrm{cm}}^{\ensuremath{-}1}$. A superconducting gap cannot be seen in our spectra.