Bose-glass melting in YBaCuO crystals with correlated disorder

We report a sharp melting transition of the Bose glass in YBaCuO crystals with columnar defects installed by the irradiation with 1 GeV Au ions. The melting BBG(T) is tracked at low fields by the irreversibility line, which undergoes a remarkable abrupt crossover at a field Bcr for the vortices aligned with columns along the c axis. Below Bcr, the upward curvature of BBG(1-T/Tc)α increases with the pin density (the exponent α grows from the clean value of ∼4/3 to ∼2 at the highest irradiation doses), in quantitative agreement with the theory of melting in the presence of correlated disorder. Above Bcr, the linear in T irreversibility line is consistent with a transition into a (super)entangled vortex liquid. © 1994 The American Physical Society.