Well-defined zigzag-shaped ramp-type Josephson junctions between ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{O}_7$ and Nb have been studied. The magnetic field dependencies of the critical currents provide evidence for $d$-wave–induced alternations in the direction of the Josephson current between neighboring sides of the zigzag structure. The arrays present controllable model systems to study the influences of $\pi$ facets in high-angle high- $T_c$ grain boundaries. From the characteristics, we estimate a possible imaginary $s$-wave admixture to the order parameter of the ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{O}_7$ to be below $1\%$.

• Received 15 August 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.057004