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 3R30deg
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 K point exhibiting nesting wave vectors in proximity to the
3 x 3R30deg 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