Moiré enhanced flat band in rhombohedral graphene

The fractional quantum anomalous Hall effect (FQAHE) is a fascinating emergent quantum state characterized by fractionally charged excitations in the absence of a magnetic field. Recently, the FQAHE has been observed in aligned rhombohedral pentalayer graphene on BN (aligned R5G/BN)¹ with moiré potential. Intriguingly, the FQAHE preferably emerges when carriers are displaced away from the moiré interface^1-3, raising debates about the role of moiré potential^4-17. Here, by performing nanospot angle-resolved photoemission spectroscopy, we directly visualize the topological flat band in both aligned and non-aligned R5G/BN. The moiré potential in the aligned sample generates moiré bands and enhances the topological flat band as compared to non-aligned sample. Combined with theoretical calculations, we propose that the moiré bands on the top surface arise through the interlayer Coulomb interaction with the moiré-modulated bottom layer. Our results provide direct experimental evidence for the role of moiré potential in aligned rhombohedral graphene, and establish a foundation for understanding its emergent quantum phenomena.