Possible spin triplet superconductivity in NaxCoO2·yH2O —59Co NMR studies
Possible spin triplet superconductivity in NaxCoO2·yH2O —59Co NMR studies
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DOI：
10.1088/0953-8984/18/2/022
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发表时间：
2003-06
期刊：
影响因子：
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通讯作者：
M. Kato;C. Michioka;T. Waki;Y. Itoh;K. Yoshimura;K. Ishida;H. Sakurai;E. Takayama-Muromachi;K. Takada;T. Sasaki
中科院分区：
文献类型：
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作者：
M. Kato;C. Michioka;T. Waki;Y. Itoh;K. Yoshimura;K. Ishida;H. Sakurai;E. Takayama-Muromachi;K. Takada;T. Sasaki
我们报道了对氧化钴超导体\(NaxCoO_2·yH_2O\)（\(T_c\sim4.7K\)）的磁性取向粉末样品的\(^{59}Co\)核磁共振（NMR）研究。从NMR谱中的二维粉末图谱来看，通过不同温度下二阶四极位移对磁场的依赖性，估算了正常态下的\(ab\)面奈特位移。在50K以下，奈特位移呈现出类似居里 - 外斯的温度依赖性，这与体磁化率\(\chi\)相似。通过对所谓的\(K - \chi\)图的分析，估算了\(K\)的自旋和轨道分量以及正的超精细耦合常数。在高达7T的外加磁场中，奈特位移中超导转变的起始温度变化不大，这与报道的较高的上临界场\(H_{c2}\)是一致的。在7T时，奈特位移在\(T_c\)以下呈现出不变的行为。在两种情况（NMR、核四极共振）下，在核自旋 - 晶格弛豫率\(1/T_1\)的温度依赖性中，在\(T_c\)正下方均未观察到相干峰。我们得出结论，\(T_c\)以下奈特位移的不变行为以及\(1/T_1\)的非常规行为可能表明具有\(p\)波或\(f\)波对称性的自旋三重态超导性。
We report 59Co NMR studies on magnetically oriented powder samples of Co oxide superconductors, NaxCoO2·yH2O, with Tc∼4.7 K. From the two-dimensional powder pattern in the NMR spectrum, the ab-plane Knight shift in the normal state was estimated from the magnetic field dependence of the 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 χ. From the analysis of the so-called K–χ plot, the spin and the orbital components of K and the positive hyperfine coupling constant were estimated. The onset temperature of the superconducting transition in the Knight shift does not change 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 behaviour below Tc. No coherence peak just below Tc was observed in the temperature dependence of the nuclear spin–lattice relaxation rate 1/T1 in either case (NMR, nuclear quadrupole resonance). We conclude that the invariant behaviour of the Knight shift below Tc and unconventional behaviours of 1/T1 may indicate spin triplet superconductivity with p- or f-wave symmetry.