Ab-Plane Anisotropy of Transport Properties in Unidirectionally Twinned YBa2Cu3O7- delta Films.

Abstract

A unidirectionally twinned, c oriented YB${\mathrm{a}}_{2}$C${\mathrm{u}}_{3}$ ${\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ film was prepared on a (001) NdGa${\mathrm{O}}_{3}$ substrate. In the normal state between 100 and 300 K, the unidirectional twin plane lattice induces a strong anisotropy of ${\ensuremath{\rho}}_{\mathrm{ab}}$, leading to a temperature independent ratio of 6 between the resisitivities across and along the twin boundaries. At 77 K, the self-field critical current parallel to twin planes is $1.2\ifmmode\times\else\texttimes\fi{}{10}^{6}\mathrm{A}/{\mathrm{cm}}^{2}$, a value which is 25 times higher than along the perpendicular direction. This shows that, at this temperature, twin boundaries control the critical current values in YBCO films by either channeling or pinning effects.