Bose-glass melting in YBaCuO crystals with correlated disorder.

We report a [ital sharp] melting transition of the Bose glass in YBaCuO crystals with columnar defects installed by the irradiation with 1 GeV Au ions. The melting [ital B][sub BG]([ital T]) is tracked at low fields by the irreversibility line, which undergoes a remarkable abrupt crossover at a field [ital B][sub cr] for the vortices aligned with columns along the [ital c] axis. Below [ital B][sub cr], the upward curvature of [ital B][sub BG][proportional to](1[minus][ital T]/[ital T][sub [ital c]])[sup [alpha]] increases with the pin density (the exponent [alpha] grows from the clean value of [similar to]4/3 to [similar to]2 at the highest irradiation doses), in quantitative agreement with the theory of melting in the presence of correlated disorder. Above [ital B][sub cr], the linear in [ital T] irreversibility line is consistent with a transition into a (super)entangled vortex liquid.