RESISTIVE LOSS AT 10 GHZ IN C-AXIC-ALIGNED IN-SITU-GROWN YBA2CU3O7 FILMS

The resistive losses near 10 GHz are measured at 4.2 K for ten {ital c}-axis-oriented YBa{sub 2}Cu{sub 3}O{sub 7} thin films deposited {ital in} {ital situ} on MgO substrates. The losses range from 16{plus minus}3 {mu}{Omega}, the lowest value reported to date for a thin film of YBa{sub 2}Cu{sub 3}O{sub 7} to 740{plus minus}150 {mu}{Omega}, a difference of more than a factor of 40. Among the same films, the dc resistivity at 100 K ranges from 50 to 155 {mu}{Omega} cm, about a factor of 3. We show that the losses in the higher-loss samples can be accounted for by the presence of small fractions of {ital c}-axis-aligned grains highly misaligned in the plane of those films. Volume fractions of highly misaligned {ital c}-axis-oriented grains as low as 4% lead to losses above 500 {mu}{Omega}, more than 25 times higher than the loss in the lowest-loss film reported here. Among the lower-loss films having less than 0.15 vol % highly misaligned grains, a substantial portion of the losses are due to additional mechanisms. Among these films, the losses are found to be lower in the films with lower normal-state resistivities and higher transition temperatures ({ital T}{sub {ital c}}). For allmore » samples, the losses increase with increasing deviations from structural or electrical behavior expected for ideal single crystals. The loss in even the lowest-loss film is orders of magnitude above that expected for an ideal isotropic BCS superconductor having the same {ital T}{sub {ital c}}. The observed loss level is consistent with the presence of a large density of uncondensed carriers.« less