Infrared Studies of Oxide Superconductors in the Normal and Superconducting States
We present a summary of the infrared properties of the cubic oxide superconductor Ba1−xKxBiO3 and the layered oxide superconductor Y1Ba2Cu3O7 in the normal and superconducting states. The normal state conductivity of Ba0.6K0.4BiO3 exhibits a broad peak near 5000cm−1 which is similar to a peak previously observed in BaPb1−xBixO3. The presence of this feature in both systems may provide an important clue to the mechanism of superconductivity in the BiO3 superconductors. The normal state conductivity of Y1Ba2Cu3O7 is characterized by a sharp temperature dependent peak near the origin and a broad mid-infrared background. This background has been interpreted both as evidence for low lying charge excitations and in terms of strong coupling between carriers and excitations of magnetic origin. In the superconducting state of Ba0.6K0.4BiO3 we obtain an energy gap of conventional magnitude. In contrast we find an extremely unconventional energy scale of 7–8kTc for the a−b plane of Y1Ba2Cu3O7 and also find evidence for substantial gap anisotropy between the a−b plane and c-axis.
KeywordsSuperconducting State Oxide Superconductor Unity Reflectivity Reflectivity Ratio Incident Electric Field
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