Ru-Knight shift measurement in the superconducting state of Sr2RuO4

Knight shift of 99 Ru (K) has been measured in the superconducting (SC) state of Sr 2 RuO 4 with T c ∼ 1.5 K. The spin component of 99 K is negative and approximately one order of magnitude larger than that of 17 O K night shift ( 17 K) in the RuO 2 plane, indicating that the Ru site feels a stronger hyperfine field originating from Ru-4d electrons. 99 K parallel to the RuO 2 plane shows no change in the SC state, in agreement with the previous 17 K results. The invariance of the spin susceptibility at both Ru and O sites in the SC state gives the decisive evidence that SC pairs are in the spin-triplet state with the SC d-vector perpendicular to the RuO 2 plane.