Magnetic field dependence of the critical current in YBa_2Cu_3O_{7-delta}/Au/Nb ramp-zigzag Josephson junctions

We study the critical current I_c dependence on applied magnetic field H for multifacet YBa_2Cu_3O_{7-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 vs. H for an 8 facet junction, forming an array of 4times(0-pi)-segments. The ramp angle is theta_r=8^circ. The facet width is 10,mum. H is applied under different angles theta relative to the substrate plane and different angles phi relative to the in-plane orientation of the zigzags. We find that a homogeneous flux distribution is only achieved for an angle theta_happrox 1^circ - 2^circ and that even a small misalignment sim 0.1^circ relative to theta_h can cause a substantial inhomogeneity of the flux density inside the junction, drastically altering its I_c vs. H interference pattern. We also show, that there is a dead angle theta^*_d relative to theta_h of similar magnitude, where the average flux density completely vanishes.