Absence of correlated flux pinning by columnar defects in irradiated epitaxial Bi 2Sr 2CaCu 2O 8 thin films

Abstract

Using heavy-ion irradiation, we produced columnar defects of different density and orientation in epitaxial Bi 2Sr 2CaCu 2O 8 thin films. Although this increases the normal state resistivity and the critical temperature is reduced proportionally to the volume fraction of damaged material, pinning-related 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 observe the absence of correlated flux pinning by columnar defects and compare to heavy-ion-irradiated single crystals and tapes, where line-like correlations have been observed.