Novel strategy for improving anisotropic critical current density of YBa2Cu3O <i>y</i> films through <i>ab</i> -plane oriented columnar defects

Abstract

We investigated the vortex pinning behaviors around the magnetic field B parallel to the ab-plane in YBa2Cu3Oy thin films with novel, ab-plane oriented columnar defects (CDs), which were successfully introduced using 200 MeV Xe ion irradiation at large angles θi = 75° − 85° from the c-axis. Critical current density Jc at B || ab was significantly enhanced when two families of inclined CDs crossed at θi = ±85°. Moreover, the crossed CDs at θi = ±85° significantly changed the drop in the exponent n of the electric field vs the current density curve (E ∝ Jn) into a broad peak for B || ab at lower temperatures. Critical scaling analyses of the transport properties indicated that the vortex glass phase formed by random pinning was dominant at B || ab, even in the presence of crossed CDs at θi = ±85°. These results are the first to demonstrate that the mechanism of the slay effect at B || ab differs from that at B || c: the crossed CDs do not induce the vortex entanglement at B || ab but do enhance Jc through the suppression of thermally activated motion of staircase vortices.