Local quantum fluctuations in kondo quasicrystal approximant Ag-In-(Ce_xY_1−x)

The ternary alloy Ag-In-Ce is the only Ce-based quasicrystal approximant showing the heavy fermion feature. Here, we report the physical properties of Ag-In-(Ce_xY₁−_x). As the Ce concentration x is diluted by the nonmagnetic element Y, the spin glass freezing temperature T_f is progressively suppressed. At T > T_f, the uniform magnetic susceptibility and electronic specific heat coefficient show χðT; xÞ-¹ ¼ α½T ζ þ θ_{e ζ ff}ðxÞ] (where α is a constant, ζ' 0.7, and θ_eff is an effective Weiss temperature) and CðT; xÞ=T ¼ β ln½T=T₀ðxÞ] (where β is a constant and T₀ is a characteristic temperature), respectively. Near the critical concentration x_c where θ_eff vanishes, χ and C=T exhibit power-law and logarithmic divergence, respectively, as T → 0. We stress that α, ζ, and β are independent of x, indicating that the T ^ζ and ln T terms come from local fluctuations that are present everywhere in the x-T phase diagram, regardless of quantum critical point. We argue that the quantum critical behavior is driven by valence fluctuations.