Surface resistance and nonlinear dynamic microwave losses of epitaxial HTS films

摘要

Many applications of high-temperature superconductor (HTS) films in microwave devices require high power-handling capabilities. Therefore we have studied the temperature and power dependence of the surface resistance R/sub s/(T,B/sub s/) of unpatterned HTS films with a very sensitive dielectric resonator technique at 19GHz. R/sub s/-values as low as 120/spl plusmn/15 /spl mu//spl Omega/ (100/spl plusmn/15 /spl mu//spl Omega/) and 760/spl plusmn/80 /spl mu//spl Omega/ (610/spl plusmn/30 /spl mu//spl Omega/) at 4.2 and 77K were obtained for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (Tl/sub 2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub 8/) films. In contrast to the small scattering in R/sub s/ at low fields, the high-field behavior varied strongly. Maximum surface magnetic fields (B/sub s/) between 1 and 15 mT (2-28 mT) were achieved at 77K (4.2K). Different loss mechanisms, like defects, heating, and intrinsic phenomena, could be identified. Besides time-domain measurements in the pulsed mode, the dynamic nature of the nonlinearities was investigated by two-tone intermodulation measurements. The very high sensitivity of this technique was applied to proof the existence of fast nonlinearities (t>100 ps) in high quality films.