Moire Dirac fermions in transition metal dichalcogenides heterobilayers

Monolayer group-VIB transition metal dichalcogenides (TMDs) feature low-energy massive Dirac fermions, which have valley contrasting Berry curvature. This nontrivial local band topology gives rise to valley Hall transport and optical selection rules for interband transitions that open up new possibilities for valleytronics. However, the large bandgap in TMDs results in relatively small Berry curvature, leading to weak valley contrasting physics in practical experiments. Here, we show that Dirac fermions with tunable large Berry curvature can be engineered in moire superlattice of TMD heterobilayers. These moire Dirac fermions are created in a magnified honeycomb lattice with its sublattice degree of freedom formed by two local moire potential minima. We show that applying an on-site potential can tune the moire flat bands into helical ones. In short-period moire superlattice, we find that the two moire valleys become asymmetric, which results in a net spin Hall current. More interestingly, a circularly polarized light drives these moire Dirac fermions into quantum anomalous Hall phase with chiral edge states. Our results open a new possibility to design the moire-scale spin and valley physics using TMD moire structures.