Dynamical magnetic susceptibility in the lamellar cobaltate superconductor NaxCoO2•yH2O

We systematically analyze the influence of the superconducting gap symmetry and the electronic structure on the dynamical spin susceptibility in superconducting NaxCoO2 center dot yH(2)O within three different models: The single a(1g)-band model with nearest-neighbor hoppings, the realistic three-band t(2g) model with, and without e(g)' pockets present at the Fermi surface. We show that the magnetic response in the normal state is dominated by the incommensurate antiferromagnetic spin density wave fluctuations at large momenta in agreement with experimental temperature dependence of the spin-lattice relaxation rate. Also, we demonstrate that the presence or the absence of the e(g)' pockets at the Fermi surface does not significantly affect this conclusion. In the superconducting state our results for d(x)(2)-y(2)- or d(xy)-wave symmetries of the superconducting order parameter are consistent with experimental data and exclude nodeless d(x)(2)-y(2)+id(xy)-wave symmetry. We further point out that the spin-resonance peak proposed earlier is improbable for the realistic band structure of NaxCoO2 center dot yH(2)O. Moreover, even if present the resonance peak is confined to the antiferromagnetic wave vector and disappears away from it.