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

Abstract

In type II superconductor, pinning centers are essential to obtain high current density, Jc. Conventional wisdom holds that highest Jc 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 Jc where pinning centers have 66% discontinuity. Furthermore, this provides record Jc, and peak irreversibility field, Hirr. The values of Jc 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 Jc is highest not where pinning potential is largest, but where the combined effects of percolation paths, critical temperature, and pinning potential, are optimized.