Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 2: Supraleitung: Dünne Schichten, Josephsonkontakte, SQUIDs I

TT 2.2: Vortrag

Montag, 11. März 2002, 10:45–11:00, H19

Nonlinear Surface Impedance of TBCCO Films — •Ermile Gaganidze¹, Roland Heidinger¹, Juergen Halbritter¹, and 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 T_C ≃ 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 Z_s 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 ≤ H_rf ≤ 10 mT. The thin Tl₂Ba₂CaCu₂O₈ films prepared by thallination of an amorphous Ba₂CaCu₂O_x precursor show already promising field dependencies δ R_s ∝ H_rfⁿ ∝ δ X_s(H_rf) with exponents n ≃ 1−2 allowing operation up to 5-7 mT. Bad spots seem to be related to δ R_s ∝ H_rf with anomalous dependencies δ R_s ∝ √H_rf/(H_rf+H₀) at µ₀ H_rf ≤ 0.3 mT hinting flow of Josephson fluxons yielding at µ₀ H_rf ≥ 0.3 mT hysteresis losses with r = δ X_s/δ R_s ≃ 1. The lateral R_s-homogeneity of the films were analyzed with an open resonator at 145 GHz.