Nonlinear surface impedance Z(T,f,H/sub rf/) of Tl-Ba-Ca-Cu-O thin films

YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) film quality has reached a stage enabling rf applications at T<80 K. Higher operating temperatures or better power handling are very much desired. Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ (Tl-2212) is a perfect candidate with its higher transition temperature T/sub c/>100 K. We studied the rf field dependence of the impedance Z/sub s/ of epitaxial Tl-2212, which shows already surface resistances at low fields superior to YBCO and promising power handling with a nonlinearity onset above (mu)/sub 0/H/sup */~=3 mT. Defective Tl-2212 films show anomalous nonlinear behavior for (mu)/sub 0/H/sub rf/<(mu)/sub 0/H/sup */~0.3 to 1 mT, extremely pronounced at T<40 K, indicating the presence of very weak-links yielding flux-flow, followed at higher fields (mu)/sub 0/H/sub rf/>=0.5 mT by hysteresis losses with a linear field dependence (delta)R/sub s/(H/sub rf/)(infininity)/H/sub rf/. Better quality Tl-2212 films show (delta)R/sub s/(H/sub rf/)(infininity)H/sub rf//sup 2/ up to fields of about 5 to 10 mT. The (delta)R/sub s/(H/sub rf/)(infinity)/H/sub rf//sup n/ (n=1,2) dependencies together with the ratios r(T)=(delta)X/sub s//(delta)R/sub s~1 to 10 hint to hysteresis losses of Josephson fluxons enhanced by slits or holes in the films.