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TT: Tiefe Temperaturen

TT 16: Anwendungen der HTSL: Hochfrequenz und Elektronik

TT 16.4: Vortrag

Donnerstag, 25. März 1999, 11:15–11:30, F1

The residual surface impedance Z(T,f,H) of YBCO and their quantitative modelling by the leakage current of weak links — •J. Halbritter — Forschungszentrum Karlsruhe, IMF1, Postfach 3640, 76021 Karlsruhe

In Nb₂O₅-junctions the critical Josephson current j_cJ(T) is accompanied by a small leakage current j_bl (∝ 1/R_bl), i.e. R_res is very small. HTS in-plane weak links show a very much reduced j_cJ(0)-value compared to theory and a large leakage current j_bl (∝ 1/R_bl) of the order of j_cJ, due to a high density of intermediate states in disordered HTS. The finite rf residual resistances R_res(T,f,H) by weak links in distanc es a_J are due to the finite normal conducting leakage current with R_bl(T<0.8T_c) ≈ const., where the R_res(T)-dependence is governed by j_cJ(T) ≈ j_cJ(1−T/T_c). Quantitative agreement experiment - model is obtained by measured values of a_J (≈ 0.2 − 20 µ m) and of j_cJ( ≈ 10² − 10⁷ A/cm²) using j_cJR_bl² ≈ 10⁻¹¹ A Ω ² cm². Aside of this agreement the T-, f- and H-dependencies R_res(T<0.8T_c,f,H) ≈ R⁰ (1+T/T_c) f^α (1+H_rf/H_c1J) are modelled quantitatively, also by a distribution of weak links (α < 2) with scaling fields H_c1J ∝ √j_cJ. Hence for HTS-samples over 7 orders of magnitude up to j_cJ ≤ 10⁷ A/cm², which is much smaller than the intrinsic critical depairing current with 4*10⁸ A/cm², extrinsic weak link properties describe R(T < 0.8 T_c,f,H) quantitatively.