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

TL;DR

This paper uses renormalization group analysis to explore how spin-valley locking and Van Hove singularities influence electronic instabilities in twisted transition metal dichalcogenides, revealing novel phases like ferromagnetism and topological superconductivity.

Contribution

It provides the first unbiased RG study of instabilities in moire TMDs considering both conventional and higher-order Van Hove singularities with spin-valley locking.

Findings

Spin-valley locking alters RG flows and leads to unexpected instabilities.

Discovery of spin- and valley-polarized ferromagnetism and topological superconductivity.

Identification of a metallic state with no symmetry breaking despite diverging susceptibility.

Abstract

Recent experiments have observed correlated insulating and possible superconducting phases in twisted homobilayer transition metal dichalcogenides (TMDs). Besides the spin-valley locked moire bands due to the intrinsic Ising spin-orbit coupling, homobilayer moire TMDs also possess either logarithmic or power-law divergent Van Hove singularities (VHS) near the Fermi surface, controllable by an external displacement field. The former and the latter are dubbed conventional and higher-order VHS, 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 moire systems, such as spin- and valley-polarized ferromagnetism and topological superconductivity with mixed parity. In particular, for the case with two higher-order VHS, 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 moire TMDs are suitable platforms to realize various interaction-induced spin-valley locked phases, highlighting physics fundamentally different from the well-studied graphene-based moire systems.