Intrinsic Surface Resistance of YBCO Thin Films Under DC Magnetic Field

We investigated the dc magnetic field and temperature dependences of the microwave intrinsic surface resistance (R_s^int) of YBa₂Cu₃O_y (YBCO) superconducting thin films with various thicknesses. We used YBCO films from 100, 200, and 300 nm thick YBCO films deposited on CeO₂/Al₂O₃ substrates. The R_s^int is means the surface resistance of YBCO film without the dielectric loss of the substrates. The R_s^int was obtained from measured surface resistance (R_s) by using a phenomenological equation. The R_s was measured using the dielectric resonator method at 21.8 GHz. A dc magnetic field of up to 5.0 T was applied parallel to the c-axis of the superconducting thin films during the R_s measurements. The R_s^int of the YBCO thin films increased when the dc magnetic field was applied. These relations could be explained with the two-fluid model for high-frequency and high-magnetic field limits. The R_s^int ratio (defined as R_s^int (5T)/R_s^int (0T)) slightly decreased with the film thickness. These results indicate that the R_s^int of HTS films depends on the film thickness in the dc magnetic field and the R_s^int in a dc magnetic field may be related to the pinning center in the HTS films.