Accurate Measurements of the Intrinsic Surface Impedance of Thin YBCO Films Using a Modified Two-tone Resonator Method

摘要

We propose a modified two-tone method that could be used for sensitivemeasurements of the intrinsic microwave surface impedance (Zs) of thinsuperconductor films and the tand of a low-loss dielectric. An open-gapresonator scheme is used to measure the penetration depth of thinsuperconductor films and extract the intrinsic Zs of the superconductor filmsfrom its measured effective surface resistance and penetration depth. We use avery small gap of 10 um between the top plate and the rest parts of theresonator. The loss tangent of rutile in the low 10^-7 range and the dielectricconstant as high as ~110 are observed at temperatures below 10 K at ~15.2 GHz,which enable to measure the Rs of the 10 mm-in-diameter YBCO films as low as\~100 micro-ohm at the same frequency (f). The discrepancy between theeffective surface resistance at ~15.2 GHz and that at ~8.5 GHz scaled to ~15.2GHz appears less than 6 % when the relations of Rs ~ f^2 and loss tangent ~ fare used. We describe usefulness of our measurement method for measuring theintrinsic microwave properties of various superconductor samples.