CRITICAL CURRENTS IN PROTON-IRRADIATED SINGLE-CRYSTAL BA2YCU3O7-DELTA

Irradiation with 3.5 MeV protons creates defects in Ba2YCu 3O7-δ, which can act as strong pinning sites, comparable to those produced by neutron irradiation. Indeed protons as well as neutrons undergo momentum-transferring collisions that result in atomic displacements; the additional electronic proton-solid interaction does not appear to yield defects which contribute to pinning. Under optimized conditions we have obtained Jc(T→0, H=1 T)∼2×107 A/cm2 in single crystals. At 77 K the value is still J c∼1.7×105 A/cm2, decreasing only threefold in a field of 6 T. The fluence and temperature dependence of J c suggest a model, in which spatially uncorrelated defects pin vortex cores.