Critical currents in vicinalYBa2Cu3O7−δfilms

Abstract

Most measurements of critical current densities in $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ thin films to date have been performed on films where the $c$ axis is grown normal to the film surface. With such films, the analysis of the dependence of the critical current, ${j}_{c}$, on the magnetic field angle is complex. The effects of extrinsic contributions to the angular field dependence of ${j}_{c}$, such as the measurement geometry and disposition of pinning centers, are convoluted with those intrinsically due to the anisotropy of the material. As a consequence of this, it is difficult to distinguish between proposed flux line lattice structure models on the basis of angular critical current density measurements on $c$-axis films. Films grown on miscut (vicinal) substrates have a reduced measurement symmetry and thus provide a greater insight into the critical current anisotropy. In this paper previous descriptions of the magnetic field angle dependence of ${j}_{c}$ in $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ are reviewed. Measurements on $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ thin films grown on a range of vicinal substrates are presented and the results interpreted in terms of the structure and dimensionality of the flux line lattice in $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. There is strong evidence for a transition in the structure of the flux line lattice depending on magnetic field magnitude, orientation, and temperature. As a consequence, a simple scaling law cannot, by itself, describe the observed critical current anisotropy in $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. The experimentally obtained ${j}_{c}(\ensuremath{\theta})$ behavior of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ is successfully described in terms of a kinked vortex structure for fields applied near parallel to the $a\text{\ensuremath{-}}b$ planes.