PRESSURE EFFECTS ON CRYSTAL ELECTRIC-FIELD EXCITATIONS IN ULTRA-LOW-CARRIER KONDO-LATTICE SYSTEMS CEP AND CEAS

Pressure effects on crystal electric field (CEF) excitations in ultra-low carrier systems CeP and CeAs have been studied up to 2.8 GPa. There are two critical pressures P-c and P-B: 0.25 GPa and 1.1 GPa for CeP, while 1.3 GPa and 2.5 GPa for CeAs, respectively. CEF excitations are well-defined for P<P-B, and there is no anomaly at the onset pressure of the ferromagnetic order, P-c. In contrast, striking anomalies have been observed around P-B. For CeP, the CEF excitation decreases to 12 meV and a new CEF excitation appears at 9 meV near P-B, then it gradually replaces the first one above P-B. For CeAs, a CEF excitation exhibits strong softening as well as broadening near P-B. Finally, the CEF spectra exhibit strong broadening around 40 K in the low temperature phase near and above P-B.