rf field dependence of surface resistance for a-b plane-textured YBa2Cn3O7-δ films deposited on copper substrate

Low rf loss at high rf field levels should be realized in order to apply high- T-c films to accelerator cavities. It is well known that c-axis perpendicular to the surface is essential to reduce R-s and its field dependence However, the effect of a-b piano texturing on R-s is not so clear because lack of experiments, especially for films deposited on metallic substrates. We developed a deposition technique that enables a-b plane texturing as well as c-axis orientation of YBCO films on a copper substrate. We prepared four samples with c-axis normal to the surface: two of them were a-b plane well textured films and the other two were a-b plane weakly textured films. The a-b plane well-textured films in low rf field exhibited a R-s higher than that of weakly textured films below 80 K. The rf field dependence measurements showed that the increase of R, with increasing rf field for the a-b plane well-textured films was slower as compared with that of the weakly textured films.