Low-energy optical properties of the nonmagnetic kagome metal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>CsV</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>
Ece Uykur, Brenden R. Ortiz, Olga Iakutkina, M. Wenzel, Stephen D. Wilson, Martin Dressel, Alexander A. Tsirlin
Abstract
Temperature-dependent reflectivity measurements on the kagome metal ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ in a broad frequency range of $50\ensuremath{-}20\phantom{\rule{0.16em}{0ex}}000\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ down to $T$=10 K are reported. The charge-density wave (CDW) formed below ${T}_{\mathrm{CDW}}$ = 94 K manifests itself in a prominent spectral-weight transfer from low to higher energy regions. The CDW gap of 60--75 meV is observed at the lowest temperature and shows significant deviations from an isotropic BCS-type mean-field behavior. Absorption peaks appear at frequencies as low as 200 ${\mathrm{cm}}^{\ensuremath{-}1}$ and can be identified with interband transitions according to density-functional calculations. The change in the interband absorption compared to ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$ reflects the inversion of band saddle points between the K and Cs compounds. Additionally, a broader and strongly temperature-dependent absorption feature is observed below 1000 ${\mathrm{cm}}^{\ensuremath{-}1}$ and assigned to a displaced Drude peak. It reflects localization effects on charge carriers.