Unusual Non-Fermi Liquid Behavior of Ce$_{1-x}$La$_{x}$Ni$_{9}$Ge$_4$ Analyzed in a Single Impurity Anderson Model with Crystal Field Effects

TL;DR

This paper investigates the non-Fermi liquid behavior of CeNi$_{9}$Ge$_4$ using a single impurity Anderson model with crystal field effects, revealing complex low-temperature phenomena related to Kondo physics and crystal field splitting.

Contribution

It introduces a detailed analysis of CeNi$_{9}$Ge$_4$'s unusual behavior using an $SU(4)$ Anderson model with crystal field effects, combining experimental data with numerical renormalization group calculations.

Findings

Record-high electronic specific heat without magnetic order.

Logarithmic specific heat increase flattens below 200 mK.

Susceptibility levels off above 200 mK and becomes constant below 1 K.

Abstract

CeNi$_{9}$Ge$_4$ exhibits unusual non-Fermi liquid behavior with the largest ever recorded value of the electronic specific heat $\Delta C/T \cong 5.5$ JK$^{-2}$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 $\Delta\chi$ levels off well above 200 mK and already becomes constant below 1 K. Furthermore, the entropy reaches 2$R$ln2 below 20 K corresponding to a four level system. An analysis of $C$ and $\chi$ 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 $\Delta c$ and $\Delta \chi$ stemming from the interplay of Kondo effect and crystal field splitting.