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.
Even after 25 years of research the pairing mechanism and - at least for electron doped compounds - also the order parameter symmetry of the high transition temperature (high-Tc) cuprate superconductors is still under debate. One of the reasons is th
e complex crystal structure of most of these materials. An exception are the infinite layer (IL) compounds consisting essentially of CuO2 planes. Unfortunately, these materials are difficult to grow and, thus, there are only few experimental investigations. Recently, we succeeded in depositing high quality films of the electron doped IL compound Sr1-xLaxCuO2 (SLCO), with x approximately 0.15, and on the fabrication of well-defined grain boundary Josephson junctions (GBJs) based on such SLCO films. Here we report on a phase sensitive study of the superconducting order parameter based on GBJ SQUIDs from a SLCO film grown on a tetracrystal substrate. Our results show that also the parent structure of the high-Tc cuprates has dx2-y2-wave symmetry, which thus seems to be inherent to cuprate superconductivity.
