Effects of 3.1-MeV proton and 1-GeV Au-ion irradiation on the magnetic flux noise and critical current ofYBa2Cu3O7−δ

We have used a dc superconducting quantum interference device to measure the spectral density of magnetic flux noise, {ital S}{sub {Phi}}({ital f}), generated by vortex motion in crystals of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) both before and after irradiation with 3.1-MeV protons and 1-GeV Au ions. In addition, we have studied the effects of irradiation on the critical current {ital J}{sub {ital c}} of the same samples. Both types of irradiation reduced {ital S}{sub {Phi}}({ital f}) at most temperatures and magnetic fields and increased {ital J}{sub {ital c}} at all temperatures and magnetic fields. By measuring {ital S}{sub {Phi}}({ital f}) versus temperature, we extract the distribution of vortex pinning energies, {ital D}({ital U}{sub 0}). Both crystals have peaks in {ital D}({ital U}{sub 0}) near 0.1 eV and 0.2 eV before irradiation, and a much reduced peak near 0.1 eV after irradiation. The noise level after either kind of irradiation was substantially higher than in an unirradiated YBCO film. {copyright} {ital 1996 The American Physical Society.}