17O NMR studies of a triangular-lattice superconductor NaxCoO2•yH2O -: art. no. 227004

We report the first O-17 NMR studies of a triangular-lattice superconductor Na(1/3)CoO(2)center dot 4/3 H2O and the host material NaxCoO2 (x=0.35 and 0.72). Knight shift measurements reveal that p-d hybridization induces sizable spin polarization in the O triangular-lattice layers. Water intercalation makes CoO2 planes homogeneous and enhances low frequency spin fluctuations near T-c=4.5 K at some finite wave vectors different from both the ferromagnetic and 120 degree modes.