Unconventional Superconductivity and Electron Correlations in Cobalt Oxyhydrate Na$_{0.35}$CoO$_{2}$$\cdot y$H$_{2}$O

T. Fujimoto; G. -q. Zheng; Y. Kitaoka; R. L. Meng; J. Cmaidalka; C. W. Chu

doi:10.1103/PhysRevLett.92.047004

paper

Unconventional Superconductivity and Electron Correlations in Cobalt Oxyhydrate Na $_{0.35}$ CoO $_{2}$ $\cdot y$ H $_{2}$ O

arXiv:cond-mat/0307127 · doi:10.1103/PhysRevLett.92.047004

Abstract

We report a precise $^{59}$ Co nuclear quadrupolar resonance (NQR) measurement on the recently discovered cobalt oxyhydrate Na $_{0.35}$ CoO $_{2}$ $\cdot y$ H $_{2}$ 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, $1/ T_{1} T = C / (T - θ)$ , with $θ$ =-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 $n ≃$ 2.2 down to $\sim$ 2.0 K but crosses over to a $1/ T_{1} \propto T$ 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.

submitted for publication in June '03

Unconventional Superconductivity and Electron Correlations in Cobalt Oxyhydrate Na0.35​CoO2​⋅yH2​O

Abstract

Unconventional Superconductivity and Electron Correlations in Cobalt Oxyhydrate Na $_{0.35}$ CoO $_{2}$ $\cdot y$ H $_{2}$ O