Effects of vortex-vortex interactions on ion-track pinning in high-T/sub c/ superconductors

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/.