Current decay from quantum tunneling of vortices in Bi-2212 superconductors

We have created randomly oriented columnar defects in textured Bi2Sr2CaCu2Ox/Ag superconducting tapes and Tl-2212 materials, using a fission process driven by irradiation with 0.8 GeV protons. Vortex pinning was significantly improved, leading to increased persistent current density J. The thermally activated decay of current with time was greatly decreased, compared with unirradiated materials. Nonetheless, temperature-independent vortex motion from quantum tunneling limits J and its stability in time. Analysis of the time-dependent studies provides estimates for the elementary vortex attempt time τ, for both as-formed and ion-processed materials.