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Anisotropic Behavior of Knight Shift in Superconducting State of NaxCoO2yH2O

Y. Ihara, K. Ishida, H. Takeya, C. Michioka, M. Kato, Y. Itoh, K. Yoshimura, K. Takada, T. Sasaki, H. Sakurai, E. Takayama-Muromachi

cond-mat.supr-conarXiv:cond-mat/0511436

Abstract

The Co Knight shift was measured in an aligned powder sample of NaxCoO2yH2O, which shows superconductivity at Tc 4.6 K. The Knight-shift components parallel (Kc) and perpendicular to the c-axis (along the ab plane Kab) were measured in both the normal and superconducting (SC) states. The temperature dependences of Kab and Kc are scaled with the bulk susceptibility, which shows that the microscopic susceptibility deduced from the Knight shift is related to Co-3d spins. In the SC state, the Knight shift shows an anisotropic temperature dependence: Kab decreases below 5 K, whereas Kc does not decrease within experimental accuracy. This result raises the possibility that spin-triplet superconductivity with the spin component of the pairs directed along the c-axis is realized in NaxCoO2yH2O.

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