Intrinsic Surface Impedance Measurement Of High Temperature Superconductor Films

High temperature superconductor films have been widely used. The devices made of high temperature superconductor films have incomparable properties, which is mainly attributed to very low intrinsic surface impedance ZS of high temperature superconductor films. It not only reflects the loss of superconductor films, but also reflects the penetration depth and superconducting energy gap, and we can directly compare the quality of different films. Therefore, measuring the intrinsic surface impedance of high temperature superconductor films correctly is of great significance.In this paper, we mainly introduce how to measure the intrinsic surface impedance of high temperature superconductor films by using the dielectric resonator method. we placed two superconductor films at each end of the cylindrical sapphire dielectric. First we can obtain the effective surface resistance by measuring the resonant frequency and the quality factor of TE012 mode and TE021 mode of the dielectric resonator. Then we let the temperature of one superconductor film rises while the rest of dielectric resonator keeps the temperature constant. We can obtain the penetration depth and the intrinsic surface impedance of the superconductor films by calculating the change of the resonant frequency of the resonator with the change of temperature.We designed and built a set of system for measuring the intrinsic impedance of superconductor films. The refrigerating machine can prevent vibration and the dielectric resonator with suspended samples can keep parallel itself while ensuring that the gap between the dielectric and the superconductor film can be adjusted to 10μm. In addition, the preliminary test showed that in the refrigerator whose power is 1.5 W@4.5 K, the temperature range of the sample stage of the dielectric resonator is 100 K - 8.5 K for the upper sample stage and 100 K - 9.5 K for the lower sample stage.We calculated the resonant frequency and geometric factor of the resonant mode that we need to measure by simulation. First of all, we measured the quality factor and resonant frequency of copper cavity to verify that the device is accurate. Then we measured the resonant frequency and quality factor of the TE012 mode and TE021 mode of the dielectric resonator composed of YBCO, and calculated the effective surface impedance of YBCO while temperature is about 15 K.