Effect of columnar defects on theJ c anisotropy of YBa2Cu3O7−δ thin films and YBa2Cu3O7−δ/PrBa2Cu3O7−δ multilayers

Epitaxial YBa2Cu3O7−δ thin films (YBCO) and YBa2Cu3O7−δ/PrBa2Cu3O7−δ multilayers (Y/Pr) were irradiated with high-energy heavy ions (770 Mev208Pb) under various directionsφ relative to thec-axis. The irradiation resulted in columnar defects tilted byφ from thec-axis. The angular dependence of their pinning activity was studied by measuring the anisotropy of the critical current density. TheJ c (B, T,ϑ) behavior of the irradiated YBCO thin films showed an additional peak, which exceeds the intrinsic pinning peak, exactly at the irradiation direction. The Y/Pr multilayers, however, showed an isotropicT c -enhancement by a factor of 5, without any additional structure in theJc(B, T,ϑ) curve.