Millimeter-wave surface resistance measurements in highly orientedYBa2Cu3O7−δthin films

Abstract

We have measured the temperature dependence of the millimeter-wave surface resistance $R_s\mathrm{}\left(T\right)\mathrm{}$ in two oriented polycrystalline thin-film samples of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$. Below 80 K, $R_s$ drops rapidly as the temperature is decreased as expected for a superconductor, but excess surface resistance is observed at low temperatures in contrast to the predictions of the Bardeen-Cooper-Schrieffer theory. The measured temperature, frequency, and orientation dependence of the surface resistance are presented and discussed.