Low-Temperature Intermediate Valence State in YbCo₂Zn₂₀

Abstract

We report 59 Co-nuclear quadrupole resonance (NQR) and 59 Co-nuclear magnetic resonance (NMR) measurements on YbCo 2 Zn 20 , which shows a giant specific heat at low temperatures. The temperature dependence of spin lattice relaxation rate reveals that Yb 4f-electrons unusually persist in a well-localized regime down to at least 0.3 K. We find NQR frequency decreases below 0.2 K corresponding to the temperature region where Fermi liquid behavior appears. The present observation through the local electric interaction suggests the static evolution of intermediate valence state even in close proximity to the localized-delocalized transition.