Twisted Type‐II Rashba Homobilayers: A Platform for Tunable Topological Moiré Flat Bands

Abstract The recent discovery of topological flat bands in twisted transition metal dichalcogenide homobilayers and multilayer graphene has sparked significant research interest. Here, a new platform for realizing tunable topological moiré flat bands: twisted type‐II Rashba homobilayers, is proposed. By maintaining centrosymmetry, the interplay between Rashba spin‐orbit coupling and interlayer interactions generates an effective pseudo‐antiferromagnetic field, opening a gap within the Dirac cone with non‐zero Berry curvature. Using twisted BiTeI bilayers as an example, it is predicted that the emergence of flat topological bands with a remarkably narrow bandwidth (below 20 meV). Notably, the system undergoes a transition from a valley Hall insulator to a quantum spin Hall insulator as the twisting angle increases. This transition arises from a competition between the twisting‐driven effective spin‐orbit coupling and sublattice onsite energies presented in type‐II Rashba moiré structures. The high tunability of Rashba materials in terms of the spin‐orbit coupling strength, interlayer interaction, and twisting angle expands the range of materials suitable for functionalizing and manipulating correlated topological properties.