Nonlinear surface impedance Z( [formula omitted]) of YBa 2Cu 3O 7 and Tl 2Ba 2CaCu 2O 8 thin films

Abstract

We study the rf field dependence of Z s of epitaxial large area (2–3 inch) YBa 2Cu 3O 7 and Tl 2Ba 2CaCu 2O 8 films using a dielectric resonator with TE 011@8.5 GHz at 4.2< T<100 K and at 0.01⩽ H rf⩽10 mT. The lateral R s-homogeneity of the films were analyzed with an open resonator at 145 GHz. Some Tl 2Ba 2CaCu 2O 8 films shows anomalous nonlinear behavior extremely pronounced at T<40 K and at μ 0 H rf⩽0.3 mT indicating the presence of very weak-links saturating already at low rf currents. At μ 0 H rf>0.3 mT the rf field dependence of all Tl 2Ba 2CaCu 2O 8 films can be described by δ R s( H rf)∝ H rf n ∝δ X s( H rf). The observed exponents n≈1–2, together with the ratios r=δ X s/δ R s∼1 hint to Josephson fluxons in weak-links.