Construction of low-loss sapphire resonators for Precise Measurements of the Microwave surface resistance of high T_c superconducting thin films

摘要

We have constructed a microwave resonator module using high T_c superconducting (HTS)thin films and a dielectric saphire 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 filme must be minimized.By reducting the parastic Q factors of the resonator module,we obtained Q values of as high as 1.2X10~7 AT 17.3K and 12GHz.From the high Q values measured in this improved resonator,the surface resistance of the YBa_2Cu_3O_y superconducting thin films on MgO substrates was calculated and found to be 0.064mohm at 20.2 K and 12GH_z.