  Layered Co oxide NaxCoO2.yH2O with the superconducting transition temperature
Tc =4.5 K has been studied by 59Co-NMR. The Knight shift K estimated from the
observed spectra for powder sample exhibits almost temperature(T)-independent
behavior above Tc and decreases with decreasing T below Tc. This result and the
existence of the coherence peak in the spin-lattice-relaxation-rate versus T
curve reported by the present authors indicate, naively speaking, that the
singlet order parameter with s-wave symmetry is realized in NaxCoO2.yH2O.
Differences of the observed behaviors between the spectra of the non-aligned
sample and the one aligned in epoxy adhesive by applying the external magnetic
field are discussed.
