Microwave properties and applications of high-TC superconducting single-crystal films

The microstrip hairpin half-wave 9-pole bandpass YBCO filter for 1.7 GHz and bandwidth of about 80 MHz has been designed and made from double-sided YBCO film on 2" sapphire substrate with CeO₂ buffer layer. The losses in the designed filter with a pass band width of 80 MHz in a copper housing at 1.7 GHz were 0.7 dB at 77 K. The observed two-peak behavior of R_s(T) dependence is a feature of the most perfect quasi-single-crystalline YBCO films, characterized by a smooth surface, low concentration of defects, large domain size and low-angle boundaries between them. In less perfect films the R_s(T) dependence is monotonous. We suppose that the two-peak character of R_s(T) observed for the first time is an intrinsic property and reveals the peculiarities of anisotropic electron pairing which can be properly described using the Boltzman kinetic equation for Bogolyubov quasiparticles.