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

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.