Screening two-dimensional materials with topological flat bands

The topological flat band (TFB) has been proposed theoretically in various lattice models, to exhibit a rich spectrum of intriguing physical behaviors. However, the experimental demonstration of flat band (FB) properties has been severely hindered by the lack of materials realization. Here, by screening materials from a first-principles materials database, we identify a group of two-dimensional materials with TFBs near the Fermi level, covering some simple line-graph and generalized line-graph FB lattice models. These include the kagome sublattice of O in TiO₂ yielding a spin-unpolarized TFB, and that of V in ferromagnetic V₃F₈ yielding a spin-polarized TFB. The monolayer Nb₃TeCl₇ and its counterparts from element substitution are found to be breathing-kagome-lattice crystals. The family of monolayer III₂VI₃ compounds exhibit a TFB representing the coloring-triangle lattice model. ReF₃, MnF₃, and MnBr₃ are all predicted to be diatomic-kagome-lattice crystals, with TFB transitions induced by atomic substitution. Finally, HgF₂, CdF₂, and ZnF₂ are discovered to host dual TFBs in the diamond-octagon lattice. Our findings pave the way to further experimental exploration of eluding FB materials and properties.