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We report NMR/NQR measurements on the hydrated cobaltate superconductor NaxCoO2*1.3H2O at elevated pressures. The spin-lattice relaxation rate (1/T1) decreases below Tc with no coherence peak [1], and is in proportion to T3 down to T~Tc/10, which provides compelling evidence for the existence of line nodes in the gap function [2,3]. The spin susceptibility obtained from the Knight shift measurement in a single crystal decreases below Tc along all crystal-axis directions [4]. These results indicate anisotropic, spin-singlet pairing, and are most consistent with a d-wave gap. The electron correlations in the normal state are antiferromagnetic-like, which increases with decreasing Na-content [1,2]. The phase diagrams of Tc, various physical properties as functions of Na-concentration [2], water content, and pressure [3] will be presented, and the inter-relation between the superconductivity and the spin correlations will be discussed.
References: [1] T. Fujimoto, G. - q. Zheng, Y. Kitaoka, R.L. Meng, J. Cmaidalka, and C.W. Chu, Phys. Rev. Lett. 92, 047004 (2004). [2] G. - q. Zheng, K. Matano, R.L. Meng, J. Cmaidalka, and C.W. Chu, J. Phys.: Condens. Matter 18, L63 (2006). [3] E. Kusano, S. Kawasaki, K. Matano, G. - q. Zheng, R.L. Meng, J. Cmaidalka, and C.W. Chu, Phys. Rev. B 76, 100506 (R) (2007). [4] G. - q. Zheng, K. Matano, D.P. Chen and C.T. Lin, Phys. Rev. B73, 180503 (R) (2006). |
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