C-axis-orientation-dependent vortex images in epitaxial thin films of YBa2Cu3O7- delta.

Abstract

Bitter decoration observations of vortices in thin films of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ with four different orientations of the c axis are reported. For moderate angles of the c-axis tilt relative to the film normal, \ensuremath{\theta}=30\ifmmode^\circ\else\textdegree\fi{} and 45\ifmmode^\circ\else\textdegree\fi{}, we find a greatly enhanced anisotropy, \ensuremath{\eta}(\ensuremath{\theta}), of the vortex magnetic dimensions, in comparison with even \ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{} in single crystals, which is attributed to the thickness dependence of the anisotropic penetration depth in films. Also, in contrast to single crystals, the anisotropy of the vortex arrangement is not proportional to \ensuremath{\eta}(\ensuremath{\theta}), in agreement with recent theoretical calculations.