Spin-valley locked instabilities in moire transition metal dichalcogenides with conventional and higher-order Van Hove singularities

Recent experiments have observed correlated insulators and possible superconductivity in twisted bilayer transition metal dichalcogenides (TMDs). Besides the spin-valley locked bands due to Ising spin-orbit coupling, homo-bilayer moire TMDs also possess either logarithmic or power-law divergent Van Hove singularities (VHS) near the Fermi surface, controllable by an external displacement field. Here, we perform a perturbative RG analysis to study the dominant instabilities in homo-bilayer TMDs for both the conventional and higher-order VHS cases. We find that the spin-valley locking largely alters the RG flows and leads to instabilities unexpected in graphene-based moire systems, such as spin- and valley-polarized phase, spin-valley density waves, and topological superconductivity with mixed parity. In particular, for the case with two higher-order VHS, we find a metallic state with no symmetry breaking despite the diverging bare susceptibility. This “super-metal-like” state arises from the constraints imposed by the spin-valley locking. Our results show how spin-valley locking significantly affects the RG analysis and demonstrate that moire TMDs are ideal platforms to realize various exotic spin-valley locked phases.