We present a combined theoretical and experimental study on the optical conductivity of ${\mathrm{CeIr}}_3{\mathrm{B}}_2$, where quasi-one-dimensional Ce chains form along the $c$ axis of the monoclinic crystal. Significant hybridization-induced features are observed along the Ce chains by broadband infrared spectroscopy, demonstrating mixed-valent behavior over a wide range of temperatures (6–300 K) and energies (up to 0.8 eV). The ferromagnetic transition at 41 K had no noticeable influence on the temperature evolution of the optical conductivity. A comparison with density functional theory plus dynamic mean-field theory calculations demonstrates the quasi-one-dimensional nature of ${\mathrm{CeIr}}_3{\mathrm{B}}_2$ and the local character of the interactions responsible for the electronic renormalization. Furthermore, we demonstrate how the spectroscopic signatures of this mixed-valent compound are captured by theory, providing a clear distinction from the response expected in the integer-valent Kondo regime.

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• Kondo effect
• Optical conductivity
• Heavy-fermion systems
• DFT+DMFT
• Fourier transform infrared spectroscopy