High-resolution Ce 3d-edge resonant photoemission study of CeNi_2

TL;DR

This study uses high-resolution resonant photoemission at the Ce 3d edge to analyze the bulk 4f electronic states in CeNi_2, revealing a Kondo resonance peak and clarifying surface versus bulk spectral features.

Contribution

It provides the first high-resolution bulk-sensitive Ce 3d-edge RPES data for CeNi_2, resolving previous controversies and confirming the applicability of the Anderson impurity model to its 4f states.

Findings

Detected a sharp Kondo resonance peak near the Fermi energy.

Identified the absence of the spin-orbit side band in bulk-sensitive spectra.

Confirmed consistency with the Anderson impurity model calculations.

Abstract

Resonant photoemission (RPES) at the Ce 3d -> 4f threshold has been performed for alpha-like compound CeNi_2 with extremely high energy resolution (full width at half maximum < 0.2 eV) to obtain bulk-sensitive 4f spectral weight. The on-resonance spectrum shows a sharp resolution-limited peak near the Fermi energy which can be assigned to the tail of the Kondo resonance. However, the spin-orbit side band around 0.3 eV binding energy corresponding to the f_{7/2} peak is washed out, in contrast to the RPES spectrum at the Ce 3d -> 4f RPES threshold. This is interpreted as due to the different surface sensitivity, and the bulk-sensitive Ce 3d -> 4f RPES spectra are found to be consistent with other electron spectroscopy and low energy properties for alpha-like Ce-transition metal compounds, thus resolves controversy on the interpretation of Ce compound photoemission. The 4f spectral weight over the whole valence band can also be fitted fairly well with the Gunnarsson-Schoenhammer calculation of the single impurity Anderson model, although the detailed features show some dependence on the hybridization band shape and (possibly) Ce 5d emissions.