Homogeneity in the Microwave Surface Resistance of Large YBa2Cu3O7−δSuperconductor Films Coated with Au

Abstract: We studied homogeneity in the microwave surface resistance of Au-coated YBa₂Cu₃O_7−δ(Au/YBCO) films. The Au/YBCO film with 4-inches in diameter was prepared in-situ with the thicknesses of 68 nm and 365 nm for the Au layer and the YBa₂Cu₃O_7−δ(YBCO) layer, respectively. We measured the effective surface resistance (R_S,eff) of the Au/YBCO film at temperatures of 25 K, 60 K, 70 K, and 77 K, respectively, at 29 different positions on the film. The R_S,effvalues were analyzed with the finite thicknesses of the Au and the YBCO layers taken into consideration. The local R_S,effvalues of the Au/YBCO film appeared to be almost uniform at 25 K. Meanwhile significant positional dependences were observed for the R_S,effof the Au/YBCO film at 60 K, 70 K and 77 K, respectively, which seemed to be due to non-uniform local penetration depth (λ) of the YBCO layer rather than due to variations in the local real-part conductivity of the YBCO layer. The observed results could not be attributed to the properties of the Au layer. At temperatures below the critical temperature of YBCO, the observed R_S,effvalues of the Au/YBCO film were significantly lower than those estimated using the surface resistance of Au and YBCO, which reflected proximity effects of the normal-metal Au layer in contact with the superconducting YBCO layer. Homogeneity in the R_S,effof the Au/YBCO film might be correlated with the distributions in the local λof the YBCO layer, providing valuable information needed for designing microwave filters. Graphic Abstract: <fig id="Figa" position="anchor"> <graphic position="anchor" specific-use="HTML" mime-subtype="PNG" href="13391_2020_212_Figa_HTML.png" id="MO10"></graphic> </fig>