Unconventional superconductivity and electron correlations in the cobalt oxyhydrate Na0.35CoO2•yH2O from nuclear quadrupole resonance -: art. no. 047004

We report a careful Co-59 nuclear quadrupolar resonance measurement on the recently discovered cobalt oxyhydrate Na0.35CoO2.yH(2)O superconductor from T=40 K down to 0.2 K. We find that in the normal state the spin-lattice relaxation rate 1/T-1 follows a Curie-Weiss type temperature (T) variation, 1/T1T=C/(T-theta), with theta=-42 K, suggesting two-dimensional antiferromagnetic spin correlations. Below T-c=3.9 K, 1/T-1 decreases with no coherence peak and follows a T-n dependence with nsimilar or equal to2.2 down to similar to2.0 K but crosses over to a 1/T(1)proportional toT variation below T=1.4 K, which suggests non-s-wave superconductivity. The data in the superconducting state are most consistent with the existence of line nodes in the gap function.