Magic angle helical quadralayer graphene: Supermoiré-Induced higher Chern flat bands

Moiré superlattices remain crucial in shaping the electronic properties of two-dimensional materials, particularly in multilayer graphene systems. Our investigation extends beyond bilayers and trilayers, embracing the complexities of structures with three or more layers. For instance, helical trilayer graphene exhibits a large magic angle and distinct Chern numbers across sublattices due to moiré-of-moiré superlattice effects. In this study, we explore helical quadralayer graphene (HQTG), computing in-plane lattice relaxation to reveal a supermoiré-scale domain structure. This domain structure supports higher Chern flat bands and uniform charge density, bringing exotic topological phenenomena and enhancing the strong coupling regime's accessibility. We further clarify the origins of the magic angle and higher Chern numbers through an detailed investigation of the geometry of the Bloch wavefunction in layer spinor space.