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

Abstract

Recent experiments have observed correlated insulating and possible superconducting phases in twisted homobilayer transition metal dichalcogenides (TMDs). Besides the spin-valley locked moir\'e bands due to the intrinsic Ising spin-orbit coupling, homobilayer moir\'e TMDs also possess either logarithmic or power-law divergent Van Hove singularities (VHSs) near the Fermi surface, controllable by an external displacement field. The former and the latter are dubbed conventional and higher-order VHSs, respectively. Here, we perform a perturbative renormalization group (RG) analysis to unbiasedly study the dominant instabilities in homobilayer 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 the corresponding extensively studied graphene-based moir\'e systems, such as spin- and valley-polarized ferromagnetism and topological superconductivity with mixed parity. In particular, for the case with two higher-order VHSs, we find a spin-valley-locking-driven metallic state with no symmetry breaking in the TMDs despite the diverging bare susceptibility. Our results show how the spin-valley locking significantly affects the RG analysis and demonstrate that moir\'e TMDs are suitable platforms to realize various interaction-induced spin-valley locked phases, highlighting physics fundamentally different from the well-studied graphene-based moir\'e systems.