Spectroscopic Signature of an Unconventional Charge-Ordered State in the Kagomé Vanadate ScV₆Sn₆

Kagomé materials are an emerging platform for studying a variety of intertwined phases, including superconductivity, charge density waves, and magnetism. Here, we report the low-energy electronic structure of the recently-discovered kagomé vanadate ScV₆Sn₆ that exhibits a charge density wave, using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) measurements. The ARPES data reveal the presence of multiple van Hove singularities (vHSs) at the M point of the Brillouin zone just below the Fermi level, but minimal changes to the electronic structure across the CDW transition. STM quasiparticle interference (QPI) measurements show strong dispersing features deep in the CDW phase. The observed QPI is inconsistent with scattering theory which assumes scattering of quasiparticles by point-like impurities that generally gives a good description of the STM QPI. Instead, reconciling the ARPES and STM measurements requires the presence of a strong momentum dependence of the scattering potential that peaks at the CDW wavevector deep in the ordered phase, which we attribute to an unconventional CDW associated with a nearby instability.