Infrared studies of AB-plane oriented YBa2Cu3O7−δ

Measurements of the infrared properties parallel to the two-dimensional conducting CuO layers of the high-Tc compound YBa2Cu3O7−δ have been carried out between 300 K and 4 K. Samples have included textured ceramics, oriented films, and small crystals. A strong, temperature-independent absorption is observed in the mid-infrared, with a temperature-dependent Drude contribution in the far infrared. 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.