Competing orders in monolayer kagome metals AV₃Sb₅

Recently, there has been a surge of studies in layered kagome metals AV₃Sb₅, where A is an alkali metal atom, including K, Rb, and Cs, as a fertile platform to explore the electron correlation effects from van Hove singularity with nontrivial topology. Here, by using first-principles and mean-field calculations, we predict that the AV₃Sb₅ monolayer can be stable and a host of strong electronic correlations from enriched van Hove singularities. We find that in the monolayer stoichiometry enforces the symmetry lowering from D_6h to D_2h, which leads to the emergence of type-II van Hove singularities. The resulting electronic structure of the monolayer features a large electronic instability, which is relieved by the inverse-star-of-David charge density wave transition with nontrivial Z₂ topology in the first-principles calculations. Correlation effects are further captured by mean-field analysis with the minimal tight-binding model. Intriguing competition physics between superconductivity and various charge density wave channels, including time-reversal symmetry broken one, is explored, demonstrating the interplay between band topology and electronic correlations. Our work suggests the existence of a new two-dimensional platform, which could help reveal the exotic van Hove physics enriched with symmetry engineering.