Upper limit of the bose-glass transition in YBa 2Cu 3O 7 at high density of columnar defects

The Bose-glass transition in YBa 2Cu 3O 7 single crystals with columnar defects produced by irradiation with 5.8 GeV Pb ions was studied both experimentally and theoretically.The Bose-glass transition line B BG (T) progressively shifts upwards with increasing doses of irradiation aφ, up to 1011 ions/cm 2.For larger φ, the B BG (T) line does not shift anymore, and saturates at B BG max (T), which is still considerably below H c 2(T).Theoretically, we show that the observed evolution of the Bose-glass transition line provides strong evidence for an intermediate or disentangled vortex liquid phase, sandwiched between the melting line B m (T) and B BG max (T), in virgin samples. © 1996 The American Physical Society.