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Possible unconventional superconductivity in Na$_x$CoO$_2$yH$_2$O probed by $μ$SR

Wataru Higemoto·Kazuki Ohishi·Akihiro Koda·Ryosuke Kadono·Kenji Ishida·Kazunori Takada·Hiroya Sakurai·Eiji Takayama-Muromachi·Takayoshi Sasaki
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Abstract

The superconducting property of recently discovered sodium cobalt oxyhydrate, Na$_{0.35}$CoO$_2$1.3H$_2$O ($T_c=4.5$ K), has been studied by means of muon spin rotation/relaxation ($μ$SR) down to 2 K. It was found that the zero-field muon spin relaxation rate is independent of the temperature, indicating that no static magnetism appears in this compound, at least above 2 K. The result also provides evidence against the breakdown of time-reversal symmetry for the superconducting order parameter. Meanwhile, the muon Knight shift at 60 kOe shows no obvious reduction below $T_c$, suggesting that the local spin susceptibility is preserved upon a superconducting transition. Considering these observations, possible unconventional superconductivity of Na$_{0.35}$CoO$_2$1.3H$_2$O is discussed.

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Wataru Higemoto, Kazuki Ohishi, Akihiro Koda, Ryosuke Kadono, Kenji Ishida, Kazunori Takada, Hiroya Sakurai, Eiji Takayama-Muromachi, Takayoshi Sasaki. 2003-10-15. Possible unconventional superconductivity in Na$_x$CoO$_2$yH$_2$O probed by $μ$SR. https://doi.org/10.1103/physrevb.70.134508

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