Superconductivity in ru-based double perovskite - The possible existence of a new superconducting pairing state

We have studied the double perovskite structure A(2)Y(RU1-xCUx)O-6 (A = Ba or Sr) system. The parent compounds are antiferromagnetic insulators. Partial substitution of the Ru-ion by Cu was found to induce superconductivity in these compounds. We also observed in these materials the coexistence of superconductivity and anomalous magnetic orders. Resistive measurements in high magnetic fields show that the field dependence of the transition temperatures is significantly different from those observed in high T-c cuprates. Our results suggest that the pairing state of these new materials may be of odd parity such as p-wave.