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
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.