Topological flat bands in functionalized arsenene monolayers

The discovery of two-dimensional nontrivial topological insulators has stimulated researchers' enthusiasm to exploit exotic topological quantum states in low dimensions. Here, we study the intriguing topological flat bands in arsenene monolayers decorated with H and transition metal magnetic atoms by using first-principles simulations and tight-binding models. Remarkably, the functionalized As monolayer can exhibit a time-reversal symmetry breaking Chern insulator (CI) with a unique topologically nontrivial flat band formed by an antibonding state of As pz and Cr d_z² orbitals. Under applying tensile strain, the As monolayer undergoes a quantum phase transition and behaves as a ferrovalley insulator (FVI). The topological quantum phase transition between CI and FVI is rationalized well by a five-orbital tight-binding model. Our work sheds light on manipulating the rare topological flat bands in layered two-dimensional quantum materials, showing opportunities for promising applications in strongly correlated topological electronics.