Competing interlayer interactions in twisted monolayer-bilayer graphene: From spontaneous electric polarization to quasi-magic angle

The family of moiré materials has become an exceptional platform for modulating interlayer couplings through the twist angle in a system with a large spatial periodicity. For trilayer graphene systems, interlayer couplings can be varied at the two interfaces, and the competition between these interactions can possibly influence the electronic structure in a significant way. In this study, we investigate the electronic properties of twisted monolayer-bilayer graphene (aAB) using first-principles calculations combined with an accurate tight-binding model. We find that at large twist angles, the electronic features in aAB are well described by the interaction between the parabolic bands of the AB-bilayer and the Dirac bands of the twisted monolayer, inducing a spontaneous electric polarization that splits the parabolic bands. As the twist angle decreases, the interlayer coupling at the twisted interface becomes dominant, making the characteristic features of aAB better described as twisted bilayer graphene (TBG) interacting with the outer Bernal layer. A moiré potential develops on the TBG-like layers and causes charge localization, while the outer Bernal layer exhibits a charge delocalization pattern with substantial sublattice polarization at the atomic scale. Additionally, we identify narrow bands with a minimum width at a quasi-magic angle of θ = 1.16°, very close to the magic angle of TBG. The localization-enhanced electron correlation in the narrow bands suggests that this system is promising for realizing correlated physics.