Critical points in heavy ion irradiated untwinned YBa2Cu3O7-δ crystals

The critical points in untwinned YBa2Cu3O7-delta crystals with dilute columnar defects an investigated. We find a convergence of a first order vortex melting line with an irreversibility line associated with the onset of the Bose glass critical regime at the lower critical point. In addition, we find that columnar defects raise the upper critical point, implying that vortex line meandering is a basic feature controlling its position.