Effect of Introduction of Artificial Pinning Center in YBa2Cu3Oy Thin Films to Reduce Surface Resistance

We investigated the effect of artificial pinning centers (APCs) in YBa 2 Cu 3 Oy (YBCO) thin films to reduce the surface resistance (Re). The introduction of APCs can increase the critical current density (Jc), so APCs are expected to decrease Re of YBCO thin films. To clarify the effect, we chose Si ion irradiation and neutron irradiation for introducing APCs. Si ions of 500 keV and 4 × 10 12 ion/cm 2 and neutrons of 1.34 × 10 12 n/cm 2 at 1 MeV conversion were irradiated in YBCO thin films with a thickness of 300 nm deposited on CeO 2 -buffered Al 2 O 3 substrates. δω and δφ of YBCO thin films without APC were less than 1.0 degree and less than 2.0 degrees, respectively, and these values were not changed very much by Si ion and neutron irradiations. Re of YBCO thin films with and without Si ion irradiation and neutron irradiation was measured using a dielectric resonator method. The applied magnetic field was up to 5T. The magnetic field dependence of R(0) e was smaller than that of R(90) e in all YBCO thin films. We found that R(90) e of Si ion irradiated and neutron irradiated YBCO thin films was reduced, and that R(90) e of Si ion irradiated thin films was about 1/3 that of unirradiated thin films at 20 K and at 5 T. In addition, R(0) e of all the YBCO thin films decreased somewhat as the magnetic field increased at 20 K. As a result, we found that the irradiation of Si ions into YBCO thin films was effective for reducing Re under a magnetic field, and it was revealed that the effect was stronger than the addition of oxide fine particles which was previously reported.