Interpretation of experimental results on Kondo systems with crystal field

TL;DR

This paper introduces a simplified method to calculate thermodynamic properties of Kondo impurities considering crystal field effects, showing good agreement with experimental data for various compounds.

Contribution

The authors extend a previous model to include orbital degeneracy and crystal field effects, improving the calculation of thermodynamic properties of Kondo systems.

Findings

Deviations below 10% without CFE for specific heat

Quantitative agreement with moderate or large CFE

Excellent fit to experimental specific heat data

Abstract

We present a simple approach to calculate the thermodynamic properties of single Kondo impurities including orbital degeneracy and crystal field effects (CFE) by extending a previous proposal by K. D. Schotte and U. Schotte [Physics Lett. A 55, 38 (1975)]. Comparison with exact solutions for the specific heat of a quartet ground state split into two doublets shows deviations below $10\%$ in absence of CFE and a quantitative agreement for moderate or large CFE. As an application, we fit the measured specific heat of the compounds CeCu$_2$Ge$_2$, CePd$_{3}$Si$_{0.3}$, CePdAl, CePt, Yb$_2$Pd$_2$Sn and YbCo$_2$Zn$_{20}$. The agreement between theory and experiment is very good or excellent depending on the compound, except at very low temperatures due to the presence of magnetic correlations (not accounted in the model).