Kondo effect in CeX$_{c}$ (X$_{c}$=S, Se, Te) studied by electrical resistivity under high pressure

TL;DR

This study investigates how high pressure influences the Kondo effect, magnetic ordering, and crystal field splitting in cerium monochalcogenides, revealing the role of $f$ state degeneracy in these phenomena.

Contribution

It provides a comprehensive analysis of pressure effects on CeX$_{c}$ compounds, highlighting the importance of $f$ state degeneracy in their electronic and magnetic behaviors.

Findings

$T_{N}$ increases then decreases with pressure, following Doniach's diagram.

Kondo effect is enhanced by pressure, evidenced by increased $ ext{ln} T$ behavior.

Crystal field splitting decreases rapidly, increasing $f$ state degeneracy.

Abstract

We have measured the electrical resistivity of cerium monochalcogenices, CeS, CeSe, and CeTe, under high pressures up to 8 GPa. Pressure dependences of the antiferromagnetic ordering temperature $T_{N}$, crystal field splitting, and the $\ln T$ anomaly of the Kondo effect have been studied to cover the whole region from the magnetic ordering regime at low pressure to the Fermi liquid regime at high pressure. $T_{N}$ initially increases with increasing pressure, and starts to decrease at high pressure as expected from the Doniach's diagram. Simultaneously, the $\ln T$ behavior in the resistivity is enhanced, indicating the enhancement of the Kondo effect by pressure. It is also characteristic in CeX$_{c}$ that the crystal field splitting rapidly decreases at a common rate of $-12.2$ K/GPa. This leads to the increase in the degeneracy of the $f$ state and further enhancement of the Kondo effect. It is shown that the pressure dependent degeneracy of the $f$ state is a key factor to understand the pressure dependence of $T_{N}$, Kondo effect, magnetoresistance, and the peak structure in the temperature dependence of resistivity.