Higher ${\rm J}_{\rm c}$ Obtained by Reduction of Pinning Potential

In type II superconductor, pinning centers are essential to obtain high current density, J_c. Conventional wisdom holds that highest J_c is obtained by using continuous columnar pinning centers, which in turn maximize pinning potential. We find this conclusion to be in severe error. Using heavy high-energy ions to insert pinning centers into the YBCO high temperature superconductor, we find peak J_c where pinning centers have 66% discontinuity. Furthermore, this provides record J_c, and peak irreversibility field, H_irr. The values of J_c achieved using discontinuous pinning centers is 5 to 60 times that achieved using continuous columnar pinning centers. We review a phenomenological theory, in its early stages, which matches this experimental result. It indicates that J_c is highest not where pinning potential is largest, but where the combined effects of percolation paths, critical temperature, and pinning potential, are optimized.