quantum criticality derived from the valence fluctuations of YbCu4Ni

In the previous works, many good crystals and nice experimental method provided a lot of subjects of the quantum critical phenomena originated from the spin. In these days, the quantum critical phenomena from the novel freedom such as the electric-quadrupole, rattling, and valence are much attracted. The prime candidate is valence. However, to study of quantum critical phenomena derived from valences, there is a large experimental problem of finding actual candidate materials. In YbCu4Ni, the valence fluctuation of Yb ion occurs from the our NQR measurement and the development of quantum fluctuations was observed with decreasing low temperatures. However, the reason for the rapid relaxation is that the intensity of the resonance line is small and it is difficult to perform ultra-low temperature measurement. muSR is suitable because the time scale is faster.