Unusual non-fermi liquid behavior of Ce1-xLaxNi9Ge4 analyzed in a single impurity Anderson model with crystal field effects

CeNi₉Ge₄ exhibits unusual non-Fermi liquid behavior with the largest ever recorded value of the electronic specific heat ∆C/T≅5.5 J K^-2 mol^-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 ∆χ levels off well above 200 mK and already becomes constant below 1 K. Furthermore, the entropy reaches 2R ln2 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 ∆c and ∆χ stemming from the interplay of Kondo effect and crystal field splitting.