Nonlinear Surface Impedance of TBCCO Films

•Ermile Gaganidze1, Roland Heidinger1, Juergen Halbritter1 und Henrik Schneidewind2
1Forschungszentrum Karlsruhe, IMF I, Postfach 3640, D-76021 Karlsruhe
2IPHT Jena, Winzerlaer Strasse 10, D-07745 Jena

Whereas YBa2Cu3O7 epitaxial film quality has reached a stage where rf applications at T £ 80 K are carried through, higher operating temperatures or higher power handling are very much desired. Tl2Ba2CaCu2O8 is a perfect candidate by its TC @ 100-105 K. Such films on MgO substrates are already successfully used in low power rf receiver filters. For high power applications, however, films on Al2O3 substrates are needed. We study the rf field dependence of Zs of epitaxial large area (2-3 inch) Tl2Ba2CaCu2O8 films on sapphire substrates using a dielectric resonator with TE011@8.5 GHz at 4.2 £ T £ 100 K and at 0.01 £ Hrf £ 10 mT. The thin Tl2Ba2CaCu2O8 films prepared by thallination of an amorphous Ba2CaCu2Ox precursor show already promising field dependencies dRs µ Hrfn µ dXs(Hrf) with exponents n @ 1-2 allowing operation up to 5-7 mT. Bad spots seem to be related to dRs µ Hrf with anomalous dependencies dRs µ Ö{Hrf/(Hrf+H0)} at m0 Hrf £ 0.3 mT hinting flow of Josephson fluxons yielding at m0 Hrf ³ 0.3 mT hysteresis losses with r = dXs/dRs @ 1. The lateral Rs-homogeneity of the films were analyzed with an open resonator at 145 GHz.