Optical study of RbV3Sb5: Multiple density-wave gaps and phonon anomalies

Temperature-dependent reflectivity studies on the nonmagnetic kagome metal RbV3Sb5 in a broad energy range (50-20000cm-1, equivalent to 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 ∼800 cm-1 (100 meV) and 360cm-1 (45 meV), the latter visible below 50 K only. Additionally, two modes at respectively 160cm-1 (20 meV) and 430cm-1 (53 meV) can be traced both above and below TCDW. They show strong anomalies already above TCDW with a further renormalization across the transition, suggesting the importance of the electron-phonon coupling in RbV3Sb5 in both normal and CDW states. While the 160cm-1 mode can be attributed to the E1u phonon, the 430cm-1 mode could not be reproduced in our phonon calculations. The antiresonance nature of this mode suggests a nontrivial electron-phonon coupling in RbV3Sb5. 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 RbV3Sb5.