Vortex pinning anisotropy in perfect YBCO films studied by transport current measurements

Critical current densities J(c) are studied for YBa2Cu3O7-delta films With J(c)(77 K) > 3MA/cm(2) in a range of applied fields, temperatures, angles b etween the field vector and the C-axis of YBCO films. Two-peaked angular J( c)(H, T) dependencies are detected. Opposite temperature behavior of J(c)(t heta)-peaks for H \\ C and H \\ ab is found. The J(c)(H \\ C)-peak first ri ses with T and then diminishes while T approaches T-irr(H). In contrast, th e J(c)(H \\ ab)-peak becomes more remarkable with temperature increase. J(c )(H, T)-curves for H \\ C-orientation exhibit two distinct crossovers, corr esponding to transitions from J(c)(H) similar to const at low fields to J(c ) proportional to H-0.5 at intermediate fields and to J(c) proportional to H-q(q similar to 1-1.5) at higher fields. Vortex interaction with linear pi n arrays is assumed to be the reason for the phenomena. (C) 2000 Elsevier S cience B.V. All rights reserved.