Flat bands in moiré lattices of transition-metal dichalcogenides have emerged as a powerful platform for exploring strongly correlated electron physics. However, the moiré flat bands in these systems caused by band folding can originate from different valleys, which complicates the physics of the flat bands. Here, we combine a band-unfolding technique with symmetry analysis to visualize how the $\mathrm{\Gamma }$ valley gives rise to flat bands for the $R$- and $H$-stacking moiré superlattices of the homobilayers. We demonstrate that the $\mathrm{\Gamma }$ valley—at the center of the Brillouin zone—interacts with its folded bands under the effect of moiré potential, then forms flat bands as the twist angle decreases. Furthermore, the topmost two $\mathrm{\Gamma }$ flat bands in $R$-stacking moiré systems maintain a robust Dirac node at the K point protected by $D_3$ symmetry. In contrast, the $\mathrm{\Gamma }$ flat bands open a gap at K in the $H$-stacking moiré superlattices due to having a $C_3$ symmetry. As a result, the change from the $R$-stacking order to the $H$-stacking order in the moiré systems causes the $\mathrm{\Gamma }$ flat bands to transform from a honeycomb lattice to a triangular lattice. The K-valley flat bands for both types of moiré superlattices exhibit similar dispersion features.

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• Electronic structure
• Twistronics
• Transition metal trichalcogenides
• First-principles calculations