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

TL;DR

This paper introduces a modified two-tone resonator method for highly sensitive measurement of the intrinsic surface impedance of thin YBCO superconducting films, enabling precise characterization at microwave frequencies.

Contribution

A novel open-gap resonator scheme with a small 10 um gap is proposed to accurately measure the intrinsic surface impedance of thin superconductor films and low-loss dielectrics at microwave frequencies.

Findings

Achieved measurement of surface resistance as low as 100 micro-ohms.

Observed loss tangent of rutile in the low 10^-7 range below 10 K.

Discrepancy between surface resistance at 15.2 GHz and 8.5 GHz is less than 6%.

Abstract

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 tand of a low-loss dielectric. An open-gap resonator scheme is used to measure the penetration depth of thin superconductor films and extract the intrinsic Zs of the superconductor films from its measured effective surface resistance and penetration depth. We use a very small gap of 10 um between the top plate and the rest parts of the resonator. The loss tangent 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 micro-ohm at the same frequency (f). The discrepancy between the effective surface resistance at ~15.2 GHz and that at ~8.5 GHz scaled to ~15.2 GHz appears less than 6 % when the relations of Rs ~ f^2 and loss tangent ~ f are used. We describe usefulness of our measurement method for measuring the intrinsic microwave properties of various superconductor samples.