Effects of In-Plane Impurity Substitution in Sr₂RuO₄

We report comparative substitution effects of nonmagnetic Ti4+ and magnetic Ir4+ impurities for Ru4+ in the spin-triplet superconductor Sr2RuO4. We found that both impurities suppress the superconductivity completely at a concentration of approximately 0.15%, reflecting the high sensitivity to translational symmetry breaking in Sr2RuO4. In addition, a rapid enhancement of residual resistivity is in quantitative agreement with unitarity-limit scattering. Our result suggests that both nonmagnetic and magnetic impurities in Sr2RuO4 act as strong potential scatterers. The behavior observed in Sr2RuO4 is similar to that of the nonmagnetic (Zn2+) impurity in the high-T-c cuprates, but different from that of the magnetic (Ni2+) impurity