Critical currents in proton-irradiated single-crystal Ba sub 2 YCu sub 3 O sub 7 minus. delta

Irradiation with 3.5 MeV protons creates defects in Ba{sub 2}YCu{sub 3}O{sub 7{minus}{delta}}, 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 {ital J}{sub {ital c}}({ital T}{r arrow}0, {ital H}=1 T){similar to}2{times}10{sup 7} A/cm{sup 2} in single crystals. At 77 K the value is still {ital J}{sub {ital c}}{similar to}1.7{times}10{sup 5} A/cm{sup 2}, decreasing only threefold in a field of 6 T. The fluence and temperature dependence of {ital J}{sub {ital c}} suggest a model, in which spatially uncorrelated defects pin vortex cores.