Unusual Nonmagnetic Ordered State in CeCoSi Revealed by ⁵⁹Co-NMR and NQR Measurements

We performed $^{59}$Co nuclear magnetic and quadrupole resonance (NMR NQR) measurements under pressure on a single-crystalline CeCoSi, which undergoes an unresolved phase transition at $T_0$. The NQR spectra clearly showed that the $T_0$ is nonmagnetic, but any symmetry lowering Co site was not seen irrespective of feature second-order transition. By contrast, NMR were split by induced field perpendicular to external field. These results show below simple paramagnetic state most likely electric multipolar ordered Ce $4f$ electrons. development Kondo effect applying thought be crucial stabilize this novel features beyond commonality tetragonal Ce-based systems.