Phonon promoted charge density wave in topological kagome metal ScV6Sn6

Abstract

Abstract Charge density wave (CDW) orders in vanadium-based kagome metals have recently received tremendous attention due to their unique properties and intricate interplay with exotic correlated phenomena, topological and symmetry-breaking states. However, the origin of the CDW order remains a topic of debate. The discovery of ScV6Sn6, a vanadium-based bilayer kagome metal exhibiting an in-plane √3 x√3 R30° CDW order with time-reversal symmetry breaking, provides a novel platform to explore the underlying mechanism behind the unconventional CDW. Here, we combine high-resolution angle-resolved photoemission spectroscopy, Raman scattering measurements and density functional theory to investigate the electronic structures and phonon modes of ScV6Sn6 and their evolution with temperature. We identify topologically nontrivial Dirac surface states and multiple van Hove singularities (VHSs) in the vicinity of the Fermi level, with one VHS near the ꝁ point exhibiting nesting wave vectors in proximity to the √3 x√3 R30° CDW wave vector. Additionally, Raman measurements indicate a strong intrinsic electron-phonon coupling in ScV6Sn6, as evidenced by the presence of a two-phonon mode and a large frequency amplitude mode. Our findings highlight the fundamental role of lattice degrees of freedom in promoting the CDW in ScV6Sn6 and provide important insights into the fascinating correlation phenomena observed in kagome metals.