CRITICAL CURRENT OF A TEXTURED YBA2CU3O7 THIN-FILM IN WEAK MAGNETIC-FIELD

V-I measurements on a superconducting and textured YBa2Cu3O7 thin film deposited on a polycrystalline BeO substrate were carried out with and without applied magnetic field at different temperatures T near Tc. The strong effect of weak magnetic fields on the critical current is interpreted by a model of superconducting percolating paths interrupted by a S-I-S Josephson junction. The values of both the penetration depth λ(T) and the superconducting gap Δ(T) are computed from this simple model. Calculations with no adjustable parameter give λ(76.5K) ≈ 1450 Å and Δ(0K) ≈ 12meV. As predicted by BCS, λ-2 and Δ2 are found to be proportional to 1-T/Tc for T near Tc. © 1990.