Electronic structure of LaTe and CeTe

Abstract

We report a comparative study of the electronic structure of the compounds LaTe and CeTe, both of which crystallize in the rock salt structure. LaTe is a paramagnetic metal while CeTe is known to exhibit anomalous Kondo-like transport behaviour and undergoes a transition to a complex magnetically ordered state at low temperature (TN=2.2K). We carry out hard X-ray photoelectron spectroscopy (HAXPES) of the core-levels and valence band of LaTe and CeTe at T=20K, in order to characterize their intrinsic electronic structure, and to address the role of Kondo effect on the electronic structure of CeTe. The bulk sensitive core level HAXPES spectra show evidence of screened features in the La 3d and Ce 3d states mixed with plasmon features. From a careful analysis of the Te, La and Ce derived core levels, we separate out the respective origins of the satellites and show that CeTe indeed exhibits definitive but weak f0 and f2 satellites due to Kondo screening, in addition to the main f1 peak. The comparison of the valence band spectra of CeTe obtained using HAXPES and soft X-ray PES clearly identifies the Ce 4f derived features. Resonant photoelectron spectrosocopy across the Ce 3d−4f threshold confirms the Ce 4f1 final state at the Fermi level, corresponding to the tail of the Kondo resonance feature which occurs above the Fermi level, while the Ce 4f0 final state feature is observed at a binding energy of 2.4eV. The 4f0 and 4f1 final states show giant resonances compared to the off-resonant spectra. However, in contrast to typical Kondo systems, the tail of the Ce 4f1 Kondo resonance at the Fermi level is relatively suppressed compared to the Ce 4f0 feature, which exhibits an unusually strong resonance enhancement. The results are indicative of a weakened Kondo effect which favours the magnetically ordered ground state in CeTe.