Strong, Asymmetric Flux Pinning by Miscut-Growth-Initiated Columnar Defects in EpitaxialYBa2Cu3O7−xFilms

Strong flux pinning and a pronounced asymmetric angular dependence of $J_c(H,\theta )$ have been discovered in ${{\mathrm{YBa}}_2{\mathrm{Cu}}_3\mathrm{O}}_{7-x}$ films grown on miscut, mosaic LaAl${\mathrm{O}}_3$ substrate surfaces. A new pinning peak, which at low fields is nearly as strong as the “intrinsic pinning,” is observed for magnetic field orientations between the $c$ axis and the Cu${\mathrm{O}}_2$ plane. Cross-section transmission electron microscopy reveals columnar growth defects (2–3 nm diameter) aligned near the $c$ axis, in concentrations $\sim {10}^{10}{\mathrm{cm}}^{-2\mathrm{}}$. The results demonstrate that deliberately modified substrate surfaces may introduce technologically useful flux pinning in ${{\mathrm{YBa}}_2{\mathrm{Cu}}_3\mathrm{O}}_{7-x}$ films.