Dependence of surface resistance in HTS thin films on a DC magnetic field

We investigated the behavior of the surface resistance (R/sub s/) of high-temperature superconductor (HTS) thin films exposed to a dc magnetic field (parallel to the c-axis). Measurements were done using the dielectric resonator method and superconducting magnet system. The DyBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (DyBCO) and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films (produced by THEVA GmbH) were prepared through a thermal co-evaporation method. The resonant frequency of the TE/sub 011/ mode in the resonator was approximately 22 GHz. A dc magnetic field of up to 5 T was applied vertically to two parallel superconducting thin films placed into a closed-type Cu cavity. R/sub s/ of the DyBCO and YBCO thin films increased as the applied dc magnetic field increased. The R/sub s/ ratio (defined as R/sub s/(5 T)/R/sub s/(0 T)) of the DyBCO and YBCO thin films at 4.5 K was approximately 5 and 50, respectively. These results indicate that the DyBCO thin film may be better for use in low-temperature nuclear magnetic resonance applications.

I. Introduction

Passive microwave components, such as filters [1]– [5] and antennas [6]– [12], are attractive target applications for high-temperature superconductors (HTSs) because the microwave loss of HTSs is significantly lower than that of normal metals. Since microwave surface resistance is closely related to the microwave loss in these devices, it is important to estimate of HTSs. There are several methods to measure of HTS thin films, in particular the microstrip line resonator technique [13] and the dielectric resonator technique [14], and we have previously applied the dielectric resonator method for the measurements [15]– [17]. The parallel plate dielectric resonator is one of the most reliable tools for measuring and it enables nondestructive measurements of HTS thin films. Therefore, this measurement technique has been designated as a standard measurement method by the International Electrotechnical Commission (IEC). Fig. 1. Schematic diagram of the measurement system.