Optical study of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>RbV</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>Sb</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:mrow></mml:math>: Multiple density-wave gaps and phonon anomalies

Abstract

Temperature-dependent reflectivity studies on the nonmagnetic kagome metal ${\mathrm{RbV}}_{3}{\mathrm{Sb}}_{5}$ in a broad energy range ($50--20000{\mathrm{cm}}^{\ensuremath{-}1}$, equivalent to 6 meV--2.5 eV) down to 10 K are reported. Below ${T}_{\mathrm{CDW}}=102$ K, the optical spectra demonstrate a prominent spectral-weight transfer from low to higher energies as the fingerprint of the charge-density-wave (CDW) formation with the opening of a partial gap. A detailed analysis reveals two energy scales of respectively $\ensuremath{\sim}800 {\mathrm{cm}}^{\ensuremath{-}1}$ (100 meV) and $360{\mathrm{cm}}^{\ensuremath{-}1}$ (45 meV), the latter visible below 50 K only. Additionally, two modes at respectively $160{\mathrm{cm}}^{\ensuremath{-}1}$ (20 meV) and $430{\mathrm{cm}}^{\ensuremath{-}1}$ (53 meV) can be traced both above and below ${T}_{\mathrm{CDW}}$. They show strong anomalies already above ${T}_{\mathrm{CDW}}$ with a further renormalization across the transition, suggesting the importance of the electron-phonon coupling in ${\mathrm{RbV}}_{3}{\mathrm{Sb}}_{5}$ in both normal and CDW states. While the $160{\mathrm{cm}}^{\ensuremath{-}1}$ mode can be attributed to the ${E}_{1u}$ phonon, the $430{\mathrm{cm}}^{\ensuremath{-}1}$ mode could not be reproduced in our phonon calculations. The antiresonance nature of this mode suggests a nontrivial electron-phonon coupling in ${\mathrm{RbV}}_{3}{\mathrm{Sb}}_{5}$. A distinct localization peak observed at all temperatures signals damped electron dynamics, whereas the reduced Drude spectral weight manifests moderate deviations from the band picture in ${\mathrm{RbV}}_{3}{\mathrm{Sb}}_{5}$.

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