Untangle charge-order dependent bulk states from surface effects in a topological kagome metal ScV_6Sn_6

Kagome metals with charge density wave (CDW) order exhibit a broad spectrum of intriguing quantum phenomena. The recent discovery of the novel kagome CDW compound ScV_6Sn_6 has spurred significant interest. However, understanding the interplay between CDW and the bulk electronic structure has been obscured by a profusion of surface states and terminations in this quantum material. Here, we employ photoemission spectroscopy and potassium dosing to elucidate the complete bulk band structure of ScV_6Sn_6, revealing multiple van Hove singularities near the Fermi level. We surprisingly discover a robust spin-polarized topological Dirac surface resonance state at the M point within the two-fold van Hove singularities. Assisted by the first-principle calculations, the temperature dependence of the k_z- resolved ARPES spectrum provides unequivocal evidence for the proposed √(3)×√(3)×3 charge order over other candidates. Our work not only enhances the understanding of the CDW-dependent bulk and surface states in ScV_6Sn_6 but also establishes an essential foundation for potential manipulation of the CDW order in kagome materials.