Hydration-induced anisotropic spin fluctuations in Na_{x}CoO_{2}\cdot1.3H_{2}O superconductor

TL;DR

This study uses ^{59}Co NMR to investigate hydration effects on spin fluctuations in Na_{x}CoO_{2}or superconductivity, hydration enhances in-plane spin fluctuations without altering the density of states, revealing quasi-two-dimensional spin correlations.

Contribution

It demonstrates that water intercalation induces anisotropic spin fluctuations in Na_{x}CoO_{2}or, highlighting the role of hydration in promoting superconductivity through spin dynamics.

Findings

Hydration enhances in-plane spin fluctuations.

Unhydrated sample behaves as a Fermi liquid.

Spin fluctuations are quasi-two-dimensional.

Abstract

We report ^{59}Co NMR studies in single crystals of cobalt oxide superconductor Na_{0.42}CoO_{2}\cdot1.3H_{2}O (T_c=4.25K) and its parent compound Na_{0.42}CoO_{2}. We find that both the magnitude and the temperature (T) dependence of the Knight shifts are identical in the two compounds above T_c. The spin-lattice relaxation rate (1/T_1) is also identical above T_0 \sim60 K for both compounds. Below T_0, the unhydrated sample is found to be a non-correlated metal that well conforms to Fermi liquid theory, while spin fluctuations develop in the superconductor. These results indicate that water intercalation does not change the density of states but its primary role is to bring about spin fluctuations. Our result shows that, in the hydrated superconducting compound, the in-plane spin fluctuation around finite wave vector is much stronger than that along the c-axis, which indicates that the spin correlation is quasi-two-dimensional.