Millimeter Wave Surface Resistance Measurements of High-Tc Superconductive Thin Flims Using A Nb Open Resonator

A hemispherical open resonator with a Nb spherical mirror has been developed to measure the surface resistance (Rs) of high-Tc superconducting films with improved sensitivity over a broad range of temperatures at W-band frequencies. Because of its open structure, the temperature of the superconducting sample can be controlled independently, while keeping the temperature of the Nb mirror at 4.2 K. We have measured the Rs of YBCO thin films successfully by this technique over a temperature range from 4.2 to 90 K at W-band frequencies. However, the estimated Rs of the spherical mirror, which was machined from a Nb rod and mechanically polished, was 70 m ¿ at 100 GHz and 4.2 K and the expected improvement in measurement sensitivity was not obtained.