Effect of magnetism and phonons on localized carriers in the ferrimagnetic kagome metals <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>GdMn</mml:mtext><mml:mn>6</mml:mn></mml:msub><mml:msub><mml:mtext>Sn</mml:mtext><mml:mn>6</mml:mn></mml:msub></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>TbMn</mml:mtext><mml:mn>6</mml:mn></mml:msub><mml:msub><mml:mtext>Sn</mml:mtext><mml:mn>6</mml:mn></mml:msub></mml:mrow></mml:math>
M. Wenzel, Alexander A. Tsirlin, Olga Iakutkina, Q. W. Yin, Hechang Lei, Martin Dressel, Ece Uykur
Abstract
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 ${\mathrm{cm}}^{\ensuremath{-}1}$, equivalent to 6.2 meV--2.23 eV) down to 10 K. At high temperatures, a phonon mode at approximately 160 ${\mathrm{cm}}^{\ensuremath{-}1}$ is observed, which becomes screened out in ${\mathrm{TbMn}}_{6}{\mathrm{Sn}}_{6}$ below $\ensuremath{\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.