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Valence and Na content dependences of superconductivity in NaxCoO2.yH2O

H. Sakurai·N. Tsujii·O. Suzuki·H. Kitazawa·G. Kido·K. Takada·T. Sasaki·E. Takayama-Muromachi
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Abstract

Various samples of sodium cobalt oxyhydrate with relatively large amounts of Na$^{+}$ ions were synthesized by a modified soft-chemical process in which a NaOH aqueous solution was added in the final step of the procedure. From these samples, a superconducting phase diagram was determined for a section of a cobalt valence of $\sim$+3.48, which was compared with a previously obtained one of $\sim$+3.40. The superconductivity was significantly affected by the isovalent exchanger of Na$^{+}$ and H$_{3}$O$^{+}$, rather than by variation of Co valence, suggesting the presence of multiple kinds of Fermi surface. Furthermore, the high-field magnetic susceptibility measurements for one sample up to 30 T indicated an upper critical field much higher than the Pauli limit supporting the validity of the spin-triplet pairing mechanism.

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H. Sakurai, N. Tsujii, O. Suzuki, H. Kitazawa, G. Kido, K. Takada, T. Sasaki, E. Takayama-Muromachi. 2005-11-17. Valence and Na content dependences of superconductivity in NaxCoO2.yH2O. https://doi.org/10.1103/physrevb.74.092502

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