Critical Current Criterion in High-T_c Superconducting Films

Abstract

Critical current densities at 77.3 K obtained by a voltage criterion of 2 µV/cm were 5.6×10 5 A/cm 2 at 0 T and 3.1×10 4 A/cm 2 at 27 T for the best Y 1 Ba 2 Cu 3 O 7-δ film prepared by chemical vapor deposition. Current-voltage curves were fitted by a power law of the form V ∝ I n with small n -values of 4–14. Since its n -value is 7 at 27 T, the J c corresponds to 2.8×10 4 A/cm 2 in the 1 µV/cm criterion and also to 2.0×10 4 A/cm 2 in the 0.1 µV/cm one. In the critical current measurement for superconducting oxides, the n -value together with the criterion should always be described.