Valence Fluctuations and Othe Correlated Electron Behavior in Yb_1-xSc_xCo₂Zn₂₀

We examine the effect of chemical pressure on YbCo₂Zn₂₀ by studying the system Yb_1-xSc_xCo₂Zn₂₀ where the smaller, non-magnetic Sc ion has been substituted for Yb. From x-ray powder diffraction measurements of the lattice constant a and magnetization measurements, we find that for low Sc content substitutions, the Yb valence v_Yb decreases linearly from 3+ at x = 0 to ~ 2.7+ x = 0.3 where v_Yb stabilizes and follows Vegard’s law for x ≥ 0.3. Resistivity measurements reveal a low-temperature upturn that can be described by a log T-dependence, consistent with the predictions of the single ion Kondo model; however, specific heat measurements cannot be fit by the resonance level model for the Kondo effect. Further analysis of C(T)/T for Yb_1-xSc_xCo₂Zn₂₀ reveal signatures consistent with non-Fermi Liquid like behavior which suggests a nearby quantum critical point (QCP). The Yb_1-xSc_xCo₂Zn₂₀ system shows a confluence of phenomena typically found in 4f electron systems including crystalline electric field effects, valence fluctuations, the Kondo effect, and heavy fermion behavior.