Unusual Non-Fermi Liquid Behavior of Ce₁₋ₓLaₓNi₉Ge₄ Analyzed in a Single Impurity Anderson Model with Crystal Field Effects

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CeNi₉Ge₄ exhibits unusual non-Fermi liquid behavior with the largest ever recorded value of the electronic specific heat ΔC/T 5.5 JK⁻²mol⁻¹ without showing any evidence of magnetic order. Specific heat measurements show that the logarithmic increase of the Sommerfeld coefficient flattens off below 200 mK. In marked contrast, the local susceptibility Δχ levels off well above 200 mK and already becomes constant below 1 K. Furthermore, the entropy reaches 2Rln2 below 20 K corresponding to a four level system. An analysis of C and χ was performed in terms of an SU(N=4) single impurity Anderson model with additional crystal electric field (CEF) splitting. Numerical renormalization group calculations point to a possible consistent description of the different low temperature scales in Δc and Δχ stemming from the interplay of Kondo effect and crystal field splitting.