Matching field effects in high-$T_{c}$ superconductors with self-assembled columnar defects

Columnar defects (CDs) in a superconductor provide angularly selective vortex pinning, where the density of CDs provides a natural scale for the magnetic field, the ``matching field.'' While dramatic changes in the critical current density $J_{c}$ might be expected when the vortex density exceeds the CD density, observations of this phenomena has been elusive in systems with chemically produced, self-assembled CDs of BaSnO$_{3}$, BaZrO$_{3}$, SrZrO$_{3}$, etc. Here we describe studies of two RBa$_{2}$Cu$_{3}$O$_{\sim 7}$ systems containing these self-avoiding CDs, using either contact free magnetic or transport measurements. In magnetic measurements on a material with measured areal CD of $\sim $2.5 T, the $J_{c}$ decreased abruptly when the applied field $H$ exceeded this level; this feature was observed over a wide temperature range, from 77 to $\sim $ 40 K. All these features disappeared when the field was tilted away from the CD orientation. Research at ORNL sponsored by US DOE.