Josephson current for a system consisting of an Anderson impurity weakly coupled to two unconventional superconductors is studied and shown to be driven by a surface zero energy (mid-gap) bound-state. The repulsive Coulomb interaction in the dot can turn a $\pi$ junction into a 0-junction. This effect is more pronounced in p-wave superconductors while in high-temperature superconductors with $d_{ x^2-y^2}$ symmetry it can exit for rather large artificial centers at which tunneling occurs within a finite region.
Categories: cond-mat.str-el