  The flat band has attracted a lot of attention because it gives rise to many
exotic phases, as recently demonstrated in magic angle twisted bilayer
graphene. Here, based on first-principles calculations, we identify a
metal-insulator transition in boron triangular Kagome lattice with a
spin-polarized flat band at 2/3-filling. This phase transition is accompanied
by the formation of a Wigner crystal, which is driven by Fermi surface nesting
effect and thereby strong electron-phonon interactions, keeping ferromagnetism.
Our calculation results suggest that boron triangular Kagome lattices with
partially filled flat bands may open a new playground for many exotic quantum
phases in two-dimensional systems, such as Winger crystallization and
fractional quantum Hall states.
