Optical Evidence of Itinerant-Localized Crossover of $4f$ Electrons in Cerium Compounds

TL;DR

This study investigates how the optical conductivity spectra of Ce-based compounds reveal the transition from itinerant to localized 4f electrons, highlighting changes near the quantum critical point through experimental and theoretical analysis.

Contribution

It provides new insights into the evolution of 4f electron behavior across the quantum critical point using optical spectroscopy and theoretical modeling.

Findings

Mid-IR peak shifts to lower energy with decreasing hybridization

Sudden high-energy shift near the quantum critical point

Electronic structure changes across the quantum critical point

Abstract

Cerium (Ce)-based heavy-fermion materials have a characteristic double-peak structure (mid-IR peak) in the optical conductivity [$\sigma(\omega)$] spectra originating from the strong conduction ($c$)--$f$ electron hybridization. To clarify the behavior of the mid-IR peak at a low $c$-$f$ hybridization strength, we compared the $\sigma(\omega)$ spectra of the isostructural antiferromagnetic and heavy-fermion Ce compounds with the calculated unoccupied density of states and the spectra obtained from the impurity Anderson model. With decreasing $c$-$f$ hybridization intensity, the mid-IR peak shifts to the low-energy side owing to the renormalization of the unoccupied $4f$ state, but suddenly shifts to the high-energy side owing to the $f$-$f$ on-site Coulomb interaction at a slight localized side from the quantum critical point (QCP). This finding gives us information on the change in the electronic structure across QCP.