Untangling Charge-Order Dependent Bulk States from Surface Effects in a Topological Kagome Metal ScV6Sn6

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