High-resolution photoemission study on low-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>T</mml:mi><mml:mi>K</mml:mi></mml:msub></mml:math>Ce systems: Kondo resonance, crystal field structures, and their temperature dependence

Abstract

We present a high-resolution photoemission study on the strongly correlated Ce compounds $\mathrm{Ce}{\mathrm{Cu}}_{6}$, $\mathrm{Ce}{\mathrm{Cu}}_{2}{\mathrm{Si}}_{2}$, $\mathrm{Ce}{\mathrm{Ru}}_{2}{\mathrm{Si}}_{2}$, $\mathrm{Ce}{\mathrm{Ni}}_{2}{\mathrm{Ge}}_{2}$, and $\mathrm{Ce}{\mathrm{Si}}_{2}$. 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 $5{k}_{B}T$ 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 noncrossing approximation (NCA), describe consistently the observed photoemission features and their temperature dependence. By fitting the NCA spectra to the experimental data and extrapolating to low temperatures, ${T}_{K}$ can be extracted quantitatively. The resulting values for ${T}_{K}$ are in excellent agreement with the results from bulk sensitive measurements, e.g., inelastic neutron scattering.