Induced point and correlated disorder pinning in untwinned YBa₂Cu₃O_7-δ crystals

The magnetic phase diagram of untwinned single crystals of YBa₂Cu₃O_7-δ is studied via transport measurements. We show that the first order vortex melting line which terminates at a critical point in high magnetic fields is strongly dependent on point disorder induced by proton irradiation. In addition, we report on the effect of heavy ion irradiation induced columnar defects on vortex pinning. We find a consistent change in the slope of the irreversibility line at the matching field and a remarkable reversal of the pinning anisotropy. Anisotropic pinning from columnar defects induced by uranium heavy ions can extend up to T_co, suggesting that even in the superconducting fluctuation regime, these defects are capable of pinning the vortex liquid.