The effect of the chaotic pinning potential on intrinsic pinning in YBa₂Cu₃O_7–δ single crystals

We study the temperature dependence of the in-plane magneto-resistance ρ_ab(T) in the untwined YBa₂Cu₃O_7–δ single crystals after irradiation by fast electrons (energy 0.5–2.5 MeV, dose 10¹⁸ cm⁻²), also with a small oxygen hypostoichiometry at different angles between the external magnetic field 15 kOe and the ab-planes α. We found that at high temperatures in the pseudogap region external magnetic field does not affect the ρ_ab(T), but it broadens transitional region T_c – T_c0 from 0.3 K at zero field and α = 0 to approximately 6 K at α = 90° in the field. In the case of an unirradiated sample, ρ_ab(T) display a 3D to 2D dimensional crossover when temperature decreases from T_c to T_c0 and scaling near the T_c0 which we relate to the flux-flow and vortex-lattice melting. The reasons for the appearance of low-temperature "tails" (paracoherent transitions) on resistive transitions corresponding to different phase regimes of the vortex matter are discussed. (author)