Construction of Low-loss Sapphire Resonators for Precise Measurements of the Microwave Surface Resistance of High T_c Superconducting Thin Films

Abstract

We have constructed a microwave resonator module using High T_c superconducting (HTS) thin films and a dielectric sapphire rod to measure microwave surface resistances of the HTS thin films. In this method the surface resistance is calculated from the measured unloaded Q values of the resonator. For precise measurements of surface resistance, therefore, the microwave loss not generated by HTS thin films must be minimized. By reducing the parasitic Q factors of the resonator module, we obtained Q values of as high as 1.2×10⁷ at 17.3K and 12GHz. From the high Q values measured in this improved resonator, the surface resistance of the YBa₂Cu₃O_y superconducting thin films on MgO substrates was calculated and found to be 0.064 mohm at 20.2K and 12GHz.