F. Hillmer et al., Absence of correlated flux pinning by columnar defects in irradiated epitaxial Bi2Sr2CaCu2O8 thin films, PHYSICA C, 311(1-2), 1999, pp. 11-18
Using heavy-ion irradiation, we produced columnar defects of different dens
ity and orientation in epitaxial Bi2Sr2CaCu2O8 thin films. Although this in
creases the normal state resistivity and the critical temperature is reduce
d proportionally to the volume fraction of damaged material, pinning-relate
d quantities like critical current density, activation energy and depinning
field are enhanced in external magnetic fields. Transport measurements in
dependence of the magnetic field and its orientation consistently indicate
two-dimensional pinning of pancake vortices at the columnar defects. We obs
erve the absence of correlated flux pinning by columnar defects and compare
to heavy-ion-irradiated single crystals and tapes, where line-like correla
tions have been observed. (C) 1999 Elsevier Science B.V. All rights reserve
d.