Experimental observation of the selection rule in Josephson coupling between In and Sr2RuO4

We have carried out experimental studies on the Josephson coupling between a conventional s-wave superconductor (In) and Sr2RuO4 and found that the coupling is allowed in the in-plane direction, but not along the c-axis. This selection rule indicates that the symmetry of superconducting order parameter of Sr2RuO4 is either p- or, alternatively, purely d-wave. If Sr2RuO4 is a p-wave superconductor, as strongly favored by other experimental evidence, our result suggests that the pairing state of Sr2RuO4 is Gamma(5)(-) with d(k) = z(k(x)+/- ky), a nodeless state in which the spins of the superconducting electrons lie in the RuO2 planes.