High Resolution Photoemission Study on Low-T_K Ce Systems: Kondo Resonance, Crystal Field Structures, and their Temperature Dependence

TL;DR

This study uses high-resolution photoemission to analyze the Kondo resonance and crystal field structures in Ce compounds, revealing temperature-dependent spectral features and accurately determining the Kondo temperature T_K.

Contribution

It introduces a normalization method to resolve spectral features up to 5 k_BT above E_F and combines experimental data with NCA calculations for quantitative T_K estimation.

Findings

Resolved Kondo resonance and crystal field structures at various temperatures.

Quantitative agreement of T_K and CF energies with neutron scattering data.

Validated theoretical spectra with experimental photoemission results.

Abstract

We present a high-resolution photoemission study on the strongly correlated Ce-compounds CeCu_6, CeCu_2Si_2, CeRu_2Si_2, CeNi_2Ge_2, and CeSi_2. Using a normalization procedure based on a division by the Fermi-Dirac distribution we get access to the spectral density of states up to an energy of 5 k_BT above the Fermi energy E_F. Thus we can resolve the Kondo resonance and the crystal field (CF) fine-structure for different temperatures above and around the Kondo temperature T_K. The CF peaks are identified with multiple Kondo resonances within the multiorbital Anderson impurity model. Our theoretical 4f spectra, calculated from an extended non-crossing approximation (NCA), describe consistently the observed photoemission features and their temperature dependence. By fitting the NCA spectra to the experimental data and extrapolating the former to low temperatures, T_K can be extracted quantitatively. The resulting values for T_K and the crystal field energies are in excellent agreement with the results from bulk sensitive measurements, e.g. inelastic neutron scattering.