Accurate Measurements of the Intrinsic Surface Impedance of Thin YBa2Cu3O7-δ Films Using a Modified Two-Tone Resonator Method.

We propose a modified two-tone method that could be used for sensitive measurements of the intrinsic microwave surface impedance (Zs) of thin superconductor films and the tanδ of a low-loss dielectric. An open-gap resonator scheme is used to measure the penetration depth (l) of thin superconductor films and extract the intrinsic Zs of the superconductor films from its measured Reseff and l. We use a very small gap of 10 μm between the top plate and the rest parts of the resonator. The tanδ of rutile in the low 10-7 range and the dielectric constant 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 μΩ at the same frequency (f). The discrepancy between the Rseff at ∼ 15.2 GHz and that at ∼ 8.5 GHz scaled to ∼ 15.2 GHz appears less than 2% when the relations of Rs ∝ f² and tanδ ∝ f are used. We describe usefulness of our measurement method for measuring the intrinsic microwave properties of various superconductor samples. [ABSTRACT FROM AUTHOR]