Volume 84, Number 5, December 2008
Article Number 57010
Number of page(s) 5
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 16 December 2008
EPL, 84 (2008) 57010
DOI: 10.1209/0295-5075/84/57010

Hydration-induced anisotropic spin fluctuations in NaxCoO2 $\cdot$ 1.3H2O superconductor

K. Matano1, C. T. Lin2 and Guo-qing Zheng1

1   Department of Physics, Okayama University - Okayama 700-8530, Japan
2   Max Planck Institute - Heisenbergstrasse 1, D-70569 Stuttgart, Germany, EU

received 11 August 2008; accepted in final form 3 November 2008; published December 2008
published online 16 December 2008

We report 59Co NMR studies in single crystals of the cobalt oxide superconductor Na0.42CoO2 $\cdot$ 1.3H2O (Tc = 4.25 K) and its parent compound Na0.42CoO2. We find that both the magnitude and the temperature (T) dependence of the Knight shifts are identical in the two compounds above Tc. The spin-lattice relaxation rate (1/T1) is also identical above T0 ~ 60 K for both compounds. Below T0, the unhydrated sample is found to be a non-correlated metal that well conforms to the Fermi liquid theory, while spin fluctuations develop in the superconductor. These results indicate that water intercalation does not change the density of states at the Fermi level or the carrier density but its primary role is to bring about spin fluctuations. Our result shows that, in the hydrated superconducting compound, the electron correlation is anisotropic. Namely, the spin fluctuation around the finite wave vector is much stronger along the a-axis direction than that along the c-axis direction.

74.25.Jb - Electronic structure.
74.70.-b - Superconducting materials.
74.25.Nf - Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.).

© EPLA 2008