Magnetic field dependence of the critical current in YBa 2 Cu 3 O 7 − δ /Au/Nb ramp-zigzag Josephson junctions

We study the critical current ${I}_{c}$ dependence on applied magnetic field $H$ for multifacet ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$/Au/Nb ramp-type zigzag Josephson junctions. For many experiments, one would like to apply a homogeneous field in the junction plane. However, even tiny misalignments can cause drastic deviations from homogeneity. We show this explicitly by measuring and analyzing ${I}_{c}$ versus $H$ for an eight-facet junction, forming an array of $4\ifmmode\times\else\texttimes\fi{}(0\ensuremath{-}\ensuremath{\pi})$ segments. The ramp angle is ${\ensuremath{\theta}}_{r}={8}^{\ensuremath{\circ}}$. $H$ is applied under different angles $\ensuremath{\theta}$ relative to the substrate plane and different angles $\ensuremath{\varphi}$ relative to the in-plane orientation of the zigzags. We find that a homogeneous flux distribution is only achieved for an angle ${\ensuremath{\theta}}_{h}\ensuremath{\approx}{1}^{\ensuremath{\circ}}--{2}^{\ensuremath{\circ}}$ and that even a small misalignment $\ensuremath{\sim}$0.1${}^{\ensuremath{\circ}}$ relative to ${\ensuremath{\theta}}_{h}$ can cause a substantial inhomogeneity of the flux density inside the junction, drastically altering its ${I}_{c}$ versus $H$ interference pattern. We also show that there is a dead angle ${\ensuremath{\theta}}_{d}^{*}$ relative to ${\ensuremath{\theta}}_{h}$ of similar magnitude, where the average flux density completely vanishes.