Untangling charge-order dependent bulk states from surface effects in a topological kagome metal ${\mathrm{ScV}}_6{\mathrm{Sn}}_6$

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 ${\mathrm{ScV}}_6{\mathrm{Sn}}_6$ 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 ${\mathrm{ScV}}_6{\mathrm{Sn}}_6$, 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 twofold van Hove singularities. Assisted by first-principles calculations, the temperature dependence of the $k_z$-resolved angle-resolved photoemission spectroscopy spectrum provides unequivocal evidence for the proposed $\sqrt{3}\times \sqrt{3}\times 3$ charge order over other candidates. Our work not only enhances the understanding of the CDW-dependent bulk and surface states in ${\mathrm{ScV}}_6{\mathrm{Sn}}_6$, but also establishes an essential foundation for potential manipulation of the CDW order in kagome materials.