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Possible Spin-triplet Superconductivity in NaxCoO2yH2O - 59Co NMR Study

M. Kato·C. Michioka·T. Waki·Y. Itoh·K. Yoshimura·K. Ishida·H. Sakurai·E. Takayama-Muromachi·K. Takada·T. Sasaki
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Abstract

We report 59Co NMR studies on the magnetically oriented powder samples of Co-oxide superconductors NaxCoO2yH2O with Tc ~ 4.7 K. From two-dimensional powder pattern in the NMR spectrum, the ab-plane Knight shift in the normal state was estimated by the magnetic field dependence of second-order quadrupole shifts at various temperatures. Below 50 K, the Knight shift shows a Curie-Weiss-like temperature dependence, similarly to the bulk magnetic susceptibility chi. From the analysis of so-called K-chi plot, the spin and the orbital components of K and the positive hyperfine coupling constant were estimated. The onset temperature of superconducting transition in the Knight shift does not change so much in an applied magnetic field up to 7 T, which is consistent with the reported high upper critical field Hc2. The Knight shift at 7 T shows an invariant behavior below Tc. No coherence peak just below Tc was observed in the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1 in both cases of NMR and NQR. We conclude that the invariant behavior of the Knight shift below Tc and unconventional behaviors of 1/T possibly indicate the spin-triplet superconductivity with p- or f-wave symmetry.

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M. Kato, C. Michioka, T. Waki, Y. Itoh, K. Yoshimura, K. Ishida, H. Sakurai, E. Takayama-Muromachi, K. Takada, T. Sasaki. 2005-07-01. Possible Spin-triplet Superconductivity in NaxCoO2yH2O - 59Co NMR Study. https://doi.org/10.1088/0953-8984%2F18%2F2%2F022

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