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首页> 外文期刊>Journal of the Physical Society of Japan >Unconventional superconductivity induced by quantum critical fluctuations in hydrate cobaltate Na-x(H3O)(z)CoO2-yH(2)O - Relationship between magnetic fluctuations and superconductivity revealed by Co nuclear quadrupole resonance
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Unconventional superconductivity induced by quantum critical fluctuations in hydrate cobaltate Na-x(H3O)(z)CoO2-yH(2)O - Relationship between magnetic fluctuations and superconductivity revealed by Co nuclear quadrupole resonance

机译：水合物钴酸盐Na-x（H3O）（z）CoO2-yH（2）O中的量子临界涨落引起的非常规超导-Co核四极共振揭示的磁涨落与超导之间的关系

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摘要

Co nuclear-quadrupole-resonance (NQR) measurements were performed on various bilayered hydrate cobaltate Na-x(H3O)(z)CoO2 center dot yH(2)O with different values of the superconducting and magnetic-ordering temperatures, T-c and T-M, respectively. From measurements of the temperature and sample dependence of the NQR frequency, it was revealed that the NQR frequency is changed by the change of the electric field gradient (EFG) along the c axis upsilon(zz) rather than the asymmetry of EFG within the ab-plane. In addition, it is considered that the change of upsilon(zz) is gaverned mainly by the trigonal distortion of the CoO2 block layers along the c axis, from the relationships between v,., and the various physical parameters. We found the tendency that samples with upsilon(zz) larger than 4.2 MHz show magnetic ordering, whereas samples with lower vzz show superconductivity. We measured the nuclear spin-lattice relaxation rate l/T-1 in these samples, and found that magnetic fluctuations depend on samples. The higher-v, sample has stronger magnetic fluctuations at T-c. From the relationship between upsilon(zz) and T-c or T-M, we suggest that the NQR frequency can be regarded as a tuning parameter to determine the ground state of the system, and develop the phase diagram using upsilon(zz). This phase diagram shows that the highest-T-c sample is located at the point where T-M is considered to be zero, which suggests that the superconductivity is induced by quantum critical fluctuations. We strongly advocate that the hydrate cobaltate superconductor presents an example of the magnetic-fluctuation-mediated superconductivity argued in the heavy-fermion compounds. The coexistence of superconductivity and magnetism observed in the sample with the highest upsilon(zz) is also discussed on the basis of the results of our experiments.
机译：在各种双层水合物钴酸盐Na-x（H3O）（z）CoO2中心点yH（2）O上以不同的超导和磁序温度值Tc和TM进行共核四极共振（NQR）测量，分别。通过测量温度和NQR频率的样本依赖性，可以发现NQR频率是通过沿c轴upsilon（zz）的电场梯度（EFG）的变化而不是由ab内EFG的不对称性来改变飞机。另外，据认为，从v和各种物理参数之间的关系来看，upsilon（zz）的变化主要是由于CoO 2块层沿c轴的三角畸变引起的。我们发现，upsilon（zz）大于4.2 MHz的样本显示出磁有序性，而vzz较低的样本显示出超导性。我们测量了这些样品中的核自旋晶格弛豫率l / T-1，发现磁波动取决于样品。较高v的样品在T-c处具有较强的磁波动。根据upsilon（zz）与T-c或T-M之间的关系，我们建议将NQR频率视为确定系统基态的调谐参数，并使用upsilon（zz）绘制相图。此相图显示最高T-c样本位于T-M被视为零的点，这表明超导电性是由量子临界波动引起的。我们强烈主张，水合钴超导体是重金属离子化合物中磁涨落介导的超导性的一个例子。在我们的实验结果的基础上，还讨论了在具有最高upsilon（zz）的样品中观察到的超导和磁性的共存。

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