Comparative study of superconducting energy gaps in oriented films and polycrystalline bulk samples of Y-Ba-Cu-O

We have made a study of infrared reflectivity from an epitaxial film of ${\mathrm{Y}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ in which the c axis is primarily oriented perpendicular to the film surface and from bulk polycrystalline samples with no orientation. In the oriented film the region of enhanced reflectivity associated with the superconducting energy gap extends to 400 ${\mathrm{cm}}^{\mathrm{-}1}$ (50 meV) compared to only 200 ${\mathrm{cm}}^{\mathrm{-}1}$ in the bulk material. We estimate the energy gap for the film to be 2Δ=(4.7±1.2)${\mathrm{kT}}_{\mathrm{c}}$, a value which is consistent with recent tunneling measurements and with strong-coupling superconductivity.