Pinning mechanism of vortices at antiphase boundaries inYBa2Cu3O7−δ

Abstract

Using quantitative magneto-optics and inversion of Biot-Savart's law for determining critical current density distributions, we investigated the anisotropic vortex pinning at planar defects in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films. Parallel oriented planar antiphase boundaries (APB's) generated in epitaxial thin films grown on vicinal ${\mathrm{SrTiO}}_{3}$ (001), serve as well defined pinning sites. This array of APB's exerts anisotropic pinning forces on vortex lines which are extraordinary high transverse to the boundary yielding a longitudinal critical current density ${j}_{c,L}$ up to $\ensuremath{\approx}30%$ of the depairing current parallel to the APB's. Remarkably, also the transverse ${j}_{c,T}$ crossing the APB's is large for smooth and sharp interfaces corresponding to values usually observed in films on well oriented single-crystalline substrates. Due to variations in the structural width of APB's the magnetic flux penetrating parallel to the defect plane exhibits a filamentary pattern at low fields. It is related to an anomalous low-field dependence of ${j}_{c,T}$ with a maximum at $\ensuremath{\approx}200 \mathrm{mT}.$ In order to distinguish different pinning mechanisms of vortices at planar defects, the angular dependence of the pinning force is calculated approximately and is compared with the experiment. The measured angular and temperature dependence as well as the magnitude of ${j}_{c,L}$ and ${j}_{c,T}$ prove that pinning at APB's is dominated by quasiparticle scattering induced variation of condensation energy, characteristic of superconductors with anisotropic order parameter.