Flux trapping and magnetic field dependence of critical currents in narrow YBCO step edge junctions

Abstract

We have studied narrow (0.8-18 /spl mu/m wide) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// step edge junctions in moderate applied magnetic fields as high as B/sub a//spl sim/25 mT. The magnetic field dependence of the junction critical current, I/sub c/, resembles a Fraunhofer diffraction pattern for all the junctions studied, although the field values of the pattern minima are modified due to the planar geometry. At 77 K these narrow junctions exhibit abrupt discontinuities in the I/sub c/(B/sub a/) pattern due to jumps in I/sub c/. These jumps are most likely due to sudden changes in the position of an individual vortex in close proximity to the junction. The I/sub c/(B/sub a/) patterns show hysteretic behaviour for applied fields B/sub a/>1-2 mT at 77 K, and the magnitude of this hysteretic behaviour appears to plateau for B/sub a/>/spl sim/12 mT, depending on junction width.