Quantum tunneling of vortices in Bi-2212 with randomly oriented columnar defects

Vortex pinning in textured Bi-2212/Ag superconducting tapes was enhanced by randomly oriented columnar defects, formed by GeV proton-induced fission of Bi-nuclei. Studies of J versus time in the range 2-40 K shows that thermally activated current decay decreased greatly. However, temperature-independent quantum tunneling of vortices considerably limits J and its temporal stability for a significant fraction of the finite-Jc region. © 2000 Elsevier Science B. V. All rights reserved.