Ru-Knight shift measurement in the superconducting state of Sr2RuO4

Knight shift of 99Ru (99K) has been measured in the superconducting (SC) state of Sr2RuO4 with Tc∼1.5 K. The spin component of 99K is negative and approximately one order of magnitude larger than that of 17O Knight shift (17K) in the RuO2 plane, indicating that the Ru site feels a stronger hyperfine field originating from Ru-4d electrons. 99K parallel to the RuO2 plane shows no change in the SC state, in agreement with the previous 17K 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 RuO2 plane