Mechanisms of limitation and nature of field dependence of critical current in HTS epitaxial YBaCuO films

Magnetic field and temperature dependencies of the critical current density, J_c(H||c, T) were measured by SQUID-magnetometry, ac magnetic susceptibility, and dc transport current techniques in the single-crystalline epitaxially-grown by off-axis dc magnetron sputtering YBa₂Cu₃O_7-δ (YBCO) films with J_c(H||c, 77 K) ≥ 2 · 10⁶ A/cm². The mechanism of vortex depinning from growth-induced linear defects, i.e., out-of-plane edge dislocations in low-angle tilt domain boundaries, is shown to describe quantitatively measured J_c(H||c, T). The developed model takes into account a statistical distribution of the dislocation domain boundaries ordered in a network as well as the interdislocation spacing within boundaries. Actual structural features of YBCO film known from HREM data turn out to be extracted from J_c(H||c, T)-curves by a fitting procedure within the proposed model.