Crossover from a three-dimensional to purely two-dimensional vortex-glass transition in deoxygenatedYBa2Cu3

Current-voltage (I-V) characteristics were used to investigate the response of the vortex-glass (VG) phase transition in high-quality epitaxial YBa_(2)Cu_(3)O_(7-δ) films in magnetic fields up to 7 T. We show that varying the oxygen content, the scaling analysis reveals a crossover from three-dimensional (3D) to a pure 2D VG transition with T_(g) = 0. At small oxygen deficiencies (7-δ = 6.75), the ρ-j curves scale according to the 3D VG model, which cannot be distinguished from a Bose-glass model from a scaling analysis with the magnetic field applied parallel to the c axis. At a lower oxygen content (7-δ = 6.48), the VG phase transition behaves analogous to the highly anisotropic Bi_(2)Sr_(2)CaCu_(2)O_(8) samples, showing a quasi-2D VG transition. For further deoxygenated samples (7-δ = 6.4), the result is consistent with a pure 2D vortex-glass model similar to that observed in the even more anisotropic Tl_(2)Ba_(2)CaCu_(2)O_(8) thin films. The estimated value of the anisotropy in high-quality oxygen-depleted samples is comparable to that of the highly anisotropic superconductors