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Spin Singlet Pairing In The Superconducting State Of Naxco02 1.3h2o: Evidence From A 59co Knight Shift In A Single Crystal, Guo-Qing Zheng, Kazuaki Matano, Dapeng Chen, C T. Lin

Australian Institute for Innovative Materials - Papers

We report a 59Co Knight-shift measurement in a single crystal of the cobalt oxide superconductor NaxCoO2∙1.3H2O (Tc=4.25 K). We find that the shift due to the spin susceptibility, Ks, is substantially large and anisotropic, with the spin shift along the a-axis Kas being two times that along the c-axis Kcs. The shift decreases with decreasing temperature (T) down to T≈100 K, then becomes a constant until superconductivity sets in. Both Kas and Kcs decrease below Tc. Our results indicate unambiguously that the electron pairing in the superconducting state is in the spin singlet form.