Variation of Pressure-Induced Valence Transition with Approximation Degree in Yb-Based Quasicrystalline Approximants

We have synthesised new Tsai-type Yb-based intermediate-valence approximant crystals (ACs) with different degrees of approximation to quasicrystals, Zn–Au–Yb 1=1 and 2=1 ACs, and investigated the external pressure effect on their Yb mean-valence ν. While 1=1 AC distinctly exhibits a first-order transition-like jump in ν at a transition pressure P_v, the 2=1 AC only exhibits an indistinct anomaly at P_v. We have also investigated the pressure dependence of the ν of the Au–Al–Yb 1=1 AC, which is a prototypal AC exhibiting pressure-induced quantum criticality. It shows a continuous valence anomaly at the critical pressure P_c, where magnetic susceptibility diverges toward zero temperature, in contrast to the valence jump in the Zn–Au–Yb 1=1 AC. These results are discussed based on a theoretical model of quantum critical valence fluctuation.