Characterize the Rs-Js dependence of HTS films

Abstract

Although many kinds of resonators have been used to measure the surface resistance (Rs) of HTS films, they may not be suitable for measuring the Rs vs. surface current (Js) dependence. The question is generated by the non-uniform Js distribution on the testing HTS film in these methods. The measured Rs is a weighted average of Rs at different Js values. The relationship between the measured Rs and Js is not clear. The aim of this work is to present a specially configured resonator to keep the Js distribution on the testing sample uniform and measure the Rs vs. Js dependence. In the method, a TE001+δ mode resonator test jig and a set of calibration procedures are used to measure the Rs of the HTS film. For small Js, the Rs of HTS film is almost independent of Js. The HTS film is fully used to achieve good measurement sensitivity. For large Js, a ring of the HTS film with almost uniform Js distribution is used to measure the Rs vs. Js dependence. The equations to calculate the Js and the Rs are derived and presented in this paper. The new method has been used to measure the Rs of YBCO film. A clearer graph of Rs vs. Js is obtained. This method solves the influence of non-uniform Js distribution and retains the sensitivity advantage of resonant method. It may provide a better solution to investigate the non-linearity of HTS film. The measured Rs vs. Js dependence is very useful for the design and analysis of non-linear HTS devices.