Reducing vortex motion in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ crystals with splay in columnar defects

A strategy to boost the current-carrying capacity of cuprate superconductors beyond the levels attainable with parallel columnar defects was recently proposed. It consists of the enforcement of vortex entanglement by controlled splay of columns. We demonstrate the validity of this suggestion in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_2$ single crystals using the difference in splay naturally occurring in irradiations with two ions differing in mass and energy. The terminal dispersion of the columns produced by 0.58-GeV ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}_{}^{30+}{}_{}{}^{}$ is about 10°, as compared with 1° for 1.08-GeV ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}_{}^{23+}{}_{}{}^{}$. At high temperatures, this large splay results in a persistent current density one order of magnitude larger and a creep rate one order of magnitude smaller.