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TT: Tiefe Temperaturen

TT 28: HF Anwendungen

TT 28.5: Vortrag

Freitag, 30. März 2001, 11:45–12:00, J

Power dependencies of the surface impedance of YBCO — •Ermile Gaganidze¹, Michael Fitsilis², Roland Heidinger¹, and Juergen Halbritter¹ — ¹Forschungszentrum Karlsruhe, IMF 1, Postfach 3640, D-76021 Karlsruhe, Germany — ²Institut fuer Elektrotechnische Grundlagen der Informatik, University of Karlsruhe, Hertzstrasse 16, D-76187 Karlsruhe, Germany

The application of HTS is obstructed by the nonlinear behavior of Z(T,f,H_rf) with rf field. The study of those nonlinearities profits by carefully calibrated rf measurements in the frequency and time domain, which yield δ R_s(H_rf) ∝ Hⁿ ∝ δ X_s (H_rf). In contrast to δ R_s(H_rf) ∝ Hⁿ, the ratio r=δ X_s/ δ R_s is independent of geometry factors and shows distinct T and f dependencies for various mechanisms and rf set-ups.

The high power rf response in the frequency domain yields nonlinear resonance curves, n and r values. The time domain measurements give useful insight about dynamics of the underlying nonlinear mechanisms. The results r ≃ 1 and n ≃ 1−2 are in line with Josephson fluxons in weak links, which may interact with dc fluxons threading through the weak links.

The weak links are quantified by R(T>T_c)-measurements with the help of percolation analysis yielding R_res (T< 0.8 T_c,f) in agreement with observations.