Kondo Effect in CeXc (Xc = S, Se, Te) Studied by Electrical Resistivity Measurements under High Pressure

We have measured the electrical resistivity of cerium monochalcogenides, CeS, CeSe, and CeTe, under high pressures of up to 8 GPa. The 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 entire 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 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 of CeXc that the crystal field splitting rapidly decreases at a common rate of -12.2K/GPa. This leads to the increase in the degeneracy of the f state and the further enhancement of the Kondo effect. It is shown that the pressure-dependent degeneracy of the f state is a key factor for understanding the pressure dependence of T-N, the Kondo effect, magnetoresistance, and the peak structure in the temperature dependence of resistivity.