Origin of Middle-Infrared Peaks in Cerium Compounds

TL;DR

This study explains the origin of mid-infrared peaks in cerium compounds' optical spectra using first-principle calculations, showing they arise from band structure effects rather than hybridization gaps.

Contribution

It demonstrates that mid-IR peaks in Ce$X_3$ compounds are due to band structure and spin-orbit effects, challenging the conventional hybridization gap interpretation.

Findings

Mid-IR peaks vary among CePd$_3$, CeSn$_3$, and CeIn$_3$.

Peaks are explained by optical transitions involving Ce 4f states.

Band structure calculations reproduce observed peak shapes.

Abstract

We have demonstrated that the middle-infrared (mid-IR) peaks in the optical conductivity spectra of Ce$X_3$ ($X$ = Pd, Sn, In) can be explained by first-principle band structure calculation with the spin-orbit interaction. The mid-IR peak shapes in these materials are not identical to one another: CePd$_3$, CeSn$_3$, and CeIn$_3$ have a triple-peak structure, double-peak structure and broad single-peak structure, respectively. These peaks can be theoretically explained by the optical transition from the occupied state to the spin-orbit splitted Ce $4f$ state. This result indicates that the mid-IR peaks originate from the simple band picture with the Ce $4f$ state near the Fermi level, not from the conventional cf hybridization gap based on the periodic Anderson model.