Kagome metals possess peculiar optical spectra consisting of contributions from free charge carriers in a Drude-type response, localized carriers seen as a strongly temperature-dependent localization peak, and, in some cases, phonons displaying strong anomalies. The rare-earth kagome metal series, $R{\mathrm{Mn}}_6{\mathrm{Sn}}_6$, provides a marvelous playground to study the electronic properties of kagome metals in the presence of variable magnetic order. Here, we report temperature-dependent reflectivity studies on two members of the $R{\mathrm{Mn}}_6{\mathrm{Sn}}_6$ family, ${\mathrm{GdMn}}_6{\mathrm{Sn}}_6$ (in-plane ferrimagnet) and ${\mathrm{TbMn}}_6{\mathrm{Sn}}_6$ (out-of-plane ferrimagnet), in a broad energy range (50–18 000 ${\mathrm{cm}}^{-1}$, equivalent to 6.2 meV–2.23 eV) down to 10 K. At high temperatures, a phonon mode at approximately 160 ${\mathrm{cm}}^{-1}$ is observed, which becomes screened out in ${\mathrm{TbMn}}_6{\mathrm{Sn}}_6$ below $\sim$150 K as the localization peak linearly passes through the mode. In ${\mathrm{GdMn}}_6{\mathrm{Sn}}_6$, the disappearance of the phonon is accompanied by the onset of saturation of the peak position, suggesting an unusual interplay between the two features.

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• Electronic structure
• Optical conductivity
• Kagome lattice
• Strongly correlated systems
• Topological materials
• Density functional theory
• Infrared spectroscopy