Unusually strong coherent response from grain-boundary Josephson network in polycrystalline Pr_xY_{1 - x}Ba₂Cu₃O_{7 - δ}

By applying a highly sensitive homemade AC susceptibility technique to Pr_xY_{1 - x}Ba₂Cu₃O_{7 - δ} polycrystals (with x = 0.0, 0.1, and 0.3), we observed very sharp Fraunhofer type low-field periodic oscillations of the real part of the AC susceptibility which were attributed to Josephson vortices penetrating intergranular regions of grain-boundary Josephson network in our samples. Assuming the Lorentz type distribution of single-junction contact areas, we were able to successfully fit the experimental data.