Critical Current Density of HTS Single Crystal YBCO Thin Films in Applied dc Field

Abstract

Magnetic field and angle dependencies of critical current density J/sub c/(H,/spl theta/) are measured for single-crystal c-oriented epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films with high J/sub c//spl ap/2 MA/cm/sup 2/ at 77 K. Films are deposited by off-axis dc magnetron sputtering onto r-cut sapphire substrates buffered with CeO/sub 2/. 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/sub c/(H) measurements start from very low fields (<0.001 T). Qualitatively different angle dependencies J/sub c/(/spl theta/) are obtained in different field ranges. Their evolution is comprehended on the base of depinning model. The "peak-effect" observed in J/sub c/(H)-dependencies at parallel magnetic field is discussed as a contribution of electromagnetic pinning.