We performed 59Co nuclear magnetic and quadrupole resonance (NMR and NQR) measurements under pressure on a single-crystalline CeCoSi, which undergoes an unresolved phase transition at T0. The NQR spectra clearly showed that the phase transition at T0 is nonmagnetic, but any symmetry lowering at the Co site was not seen irrespective of the feature of second-order phase transition. By contrast, the NMR spectra were split by the induced magnetic field perpendicular to the external magnetic field. These results show that the phase below T0 is not a simple paramagnetic state but is most likely electric multipolar ordered state of Ce 4 f electrons. The development of the Kondo effect by applying pressure is thought to be crucial to stabilize this state and to show novel features beyond commonality of tetragonal Ce-based systems.

中文翻译：

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59Co-NMR 和 NQR 测量揭示了 CeCoSi 中不寻常的非磁性有序状态

我们在压力下对单晶 CeCoSi 进行了 59Co 核磁和四极共振（NMR 和 NQR）测量，该单晶 CeCoSi 在 T0 处经历了未解析的相变。NQR 谱清楚地表明 T0 处的相变是非磁性的，但无论二阶相变的特征如何，都没有看到 Co 位点的任何对称性降低。相比之下，NMR 谱被垂直于外部磁场的感应磁场分开。这些结果表明，T0 以下的相不是简单的顺磁态，而是最有可能是 Ce 4 f 电子的电多极有序态。通过施加压力来发展 Kondo 效应被认为对于稳定这种状态和显示超出四方 Ce 基系统通用性的新特征至关重要。