Physical Review Letters

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

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We have made a study of infrared reflectivity from an epitaxial film of Y1Ba2Cu3O7-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 cm-1 (50 meV) compared to only 200 cm-1 in the bulk material. We estimate the energy gap for the film to be 2"=(4.7±1.2)kTc, a value which is consistent with recent tunneling measurements and with strong-coupling superconductivity. © 1987 The American Physical Society.