ANISOTROPIC VORTEX DYNAMICS AND PHASE-DIAGRAM OF YBA2CU3O7 SINGLE-CRYSTALS WITH CANTED COLUMNAR DEFECTS

The anisotropic vortex dynamics and phase diagram are determined for a YBa2Cu3O7 single crystal with columnar defects oriented at +/-7.5 deg rees relative to the crystalline c-axis. A second-order splayed-glass to vortex-liquid transition is manifested for magnetic fields nearly p arallel to the columns via the critical scaling of vortex AC and DC tr ansport properties. In contrast, for magnetic fields aligned close to the ab-plane, an XY-like vortex-glass transition prevails. For magneti c fields at intermediate angles, there is no evidence of any vortex ph ase transition, and the vortex dynamics is described in terms of the t hermally activated flux flow model.