Optical study of RbV$_3$Sb$_5$: Multiple density-wave gaps and phonon anomalies

Abstract

Temperature-dependent reflectivity studies on the non-magnetic kagome metal RbV3Sb5 in a broad energy range (50 cm −1 -20000 cm −1 ; 6 meV -2.5 eV) down to 10 K are reported. Below TCDW=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, ∼ 100 meV and 45 meV, the latter appearing only below 50 K. Additionally, two modes at, respectively, 160 cm −1 and 430 cm −1 can be traced over the whole measured temperature range. Strong anomalies are observed for both of these modes already above TCDW with a further renormalization across TCDW, suggesting the importance of the electron-phonon coupling in RbV3Sb5 in both normal and CDW states. While the 160 cm −1 mode can be attributed to the E1u phonon, the 430 cm −1 mode could not be reproduced in our phonon calculations. The antiresonance nature of this mode gives hints for a nontrivial electron-phonon coupling in RbV3Sb5.