Temperature-dependent $f$-electron evolution in CeCoIn$_5$ via a comparative infrared study with LaCoIn$_5$

TL;DR

This study uses infrared spectroscopy to compare CeCoIn$_5$ and LaCoIn$_5$, revealing the temperature-dependent evolution of $f$ electrons and hybridization gaps in CeCoIn$_5$, with implications for understanding $f$-electron systems.

Contribution

It introduces a comparative infrared spectroscopy method to analyze $f$-electron evolution and hybridization gaps in CeCoIn$_5$, highlighting temperature-dependent electronic changes.

Findings

The $f$ electrons significantly affect low-energy optical spectra at low temperatures.

The onset of the Kondo effect occurs at temperatures higher than previously known.

CeCoIn$_5$ has a hybridization gap distribution with two main components.

Abstract

We investigated CeCoIn$_5$ and LaCoIn$_5$ single crystals, which have the same HoCoGa$_5$-type tetragonal crystal structure, using infrared spectroscopy. However, while CeCoIn$_5$ has 4$f$ electrons, LaCoIn$_5$ does not. By comparing these two material systems, we extracted the temperature-dependent electronic evolution of the $f$ electrons of CeCoIn$_5$. We observed that the differences caused by the $f$ electrons are more obvious in low-energy optical spectra at low temperatures. We introduced a complex optical resistivity and obtained a magnetic optical resistivity from the difference in the optical resistivity spectra of the two material systems. From the temperature-dependent average magnetic resistivity, we found that the onset temperature of the Kondo effect is much higher than the known onset temperature of Kondo scattering ($\simeq$ 200 K) of CeCoIn$_5$. Based on momentum-dependent hybridization, the periodic Anderson model, and a maximum entropy approach, we obtained the hybridization gap distribution function of CeCoIn$_5$ and found that the resulting gap distribution function of CeCoIn$_5$ was mainly composed of two (small and large) components (or gaps). We assigned the small and large gaps to the in-plane and out-of-plane hybridization gaps, respectively. We expect that our results will provide useful information for understanding the temperature-dependent electronic evolution of $f$-electron systems near Fermi level.