Many superconductor applications rely on the ability to pin vortex lattices. This ability depends on structural defects to pin individual vortices, but vortex-vortex interactions often play an important role in pinning the other vortices. Experimental progress on this complex problem can be made by introducing random arrays of well-defined pinning centers and studying the flux dynamics for a range of vortex densities (i.e., fields). The results of such studies in epitaxial Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub y/ films containing ion tracks show the importance of vortex-vortex interactions. As an example, the effective pinning field of the defects rises to many times the ion-dose field for temperatures well below T/sub c/.

Dissipation and critical current densities in high-Tc superconductors can depend on both intragranular flux creep and intergranular weak links. Separating these effects in polycrystals can be a formidable task. We present current-voltage data which can in some cases identify weak-link , and verify it by using ion irradiation to greatly diminish the contribution from flux creep. We conclude that the occurrence of significant weak links in series with so-called strongly-coupled current paths may be more common than previously deduced.