Magnetoresistance and Intrinsic Pinning of Vortices in the Untwinned YBa2Cu3O7 - δ Single Crystals with Optimal Oxygen Content and a Small Deviation from the Oxygen Stoichiometry

R.V. Vovka, V.M. Gvozdikova, M.A. Obolenskiia, Z.F. Nazyrova, and V.V. Kruglyakb aKharkov National University, 4 Svoboda Sq., 61077 Kharkov, Ukraine bUniversity of Exeter, Stocker Road, Exeter, EX4 4QL, United Kingdom

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We study the temperature dependence of the in-plane magnetoresistance ρab (T) in untwinned YBa2Cu3O7 - δ single crystals with the optimal oxygen content and with a small deficit of oxygen atoms 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 ρab (T) but it broadens transitional region Tc - Tc0 from 0.3 K at zero field and α = 0 to approximately 6 K at α = 60° in the field. In case of optimal doping the function ρab (T) display a 3D to 2D dimensional crossover when temperature decreases from Tc to Tc0 and scaling near the Tc0 which we relate to the flux-flow and vortex-lattice melting. In the underdoped sample the vortices are effectively pinned by the random oxygen vacancies and the function ρab (T) in transitional region has smooth tails without any traces of crossover and scaling.

DOI: 10.12693/APhysPolA.121.1191 PACS numbers: 74.25.Fy, 74.25.Qt