Suppression of superconductivity in Sr2RuO4 caused by defects

We have investigated depairing effects in Sr2RuO4, the unconventional superconductor in the layered perovskite structure. We prepared crystals of Sr2RuO4 with very low levels of impurity elements, and systematically controled their superconducting transition temperature T-c ranging from 1.5 to 0.6 K by adjustments of crystal growth conditions. The dependence of T-c on the residual resistivity po in these crystals suggests that the defects are strong pair breakers,in addition to impurities. We further characterized the effects of pair breaking in this unconventional superconductor. We found that the in-plane coherence length xi(ab)(0) evaluated from H-c2(T) is inversely proportional to T-c, and decreases with increasing mean free path I; the latter behavior is opposite to that of conventional superconductors. In addition, we examined the temperature dependence of NrlHe which substantially deviates from the ECS theory and even from a recent theory of a p-wave superconductor. [S0163-1829(99)11225-6].