Introducing Artificial Pinning Centers Into YBCO Thin Films to Improve Surface Resistance in a DC Magnetic Field

We investigated the effect of introducing artificial pinning centers (APCs) into YBa₂Cu₃O_7-δ (YBCO) thin films to reduce the microwave surface resistance (R_s) in a high dc magnetic field for high-performance microwave devices with high-quality factor (Q). YBCO thin films with and without APCs were deposited on MgO(100) substrates by using the pulsed laser deposition technique. We used commercial 0, 1.5, 3.0 wt% BaMO₃ (BMO, M = Zr, Hf) doped YBCO targets. The δω and δφ of the YBCO thin films increased as BMO doping increased, and the rate of increase appeared to be smaller for BHO doping than for BZO doping. The R_s of these thin films was measured at 21.8 GHz with the dielectric resonator method and a dc magnetic field of up to 5.0 T was applied parallel to the c-axis of the YBCO thin films during the R_s measurements. The R_s of the BMO doped films in the magnetic field was smaller than that of the pure YBCO films. In particular the R_s of the 1.5 wt% BHO doped films was the smallest among all of the films, about half compared with that of the R_s of the pure YBCO films at 4 T and 20 K. As a result, we found that introducing APCs into YBCO thin films is effective for decreasing R_s under a dc magnetic field.