Critical current density of HTS single crystal YBCO thin films in applied dc field

Magnetic field and angle dependencies of critical current density J_c(H,θ) are measured for single-crystal c-oriented epitaxial YBa₂Cu₃O_7-δ thin films with high J_c≈2 MA/cm² at 77 K. Films are deposited by off-axis dc magnetron sputtering onto r-cut sapphire substrates buffered with CeO₂. Experimental evidences of the dominant contribution of extended linear defects (growth-induced out-of-plane edge dislocations) to pinning mechanism and critical current behavior are presented. A consistent model of vortex lattice depinning from a linear defect system is developed. Detailed J_c(H) measurements start from very low fields (<0.001 T). Qualitatively different angle dependencies J_c(θ) are obtained in different field ranges. Their evolution is comprehended on the base of depinning model. The "peak-effect" observed in J_c(H)-dependencies at parallel magnetic field is discussed as a contribution of electromagnetic pinning.