Orientation-tunable correlated Chern insulating states in chiral twisted double bilayer graphene proximitized by WSe2

Abstract

Moiré flat bands in graphene systems proximitized by transition-metal dichalcogenides (TMDCs) provide a setting where spin-orbit coupling (SOC) can reshape band topology. The crystallographic alignment angle Φ between TMDC and graphene layers is predicted to tune the balance of Ising and Rashba SOC, but a combined theoretical and experimental understanding of how Φ governs the topological character of correlated states has not been systematically established. Here we show that in chiral-stacked twisted double bilayer graphene in proximity to WSe2, Φ determines the topological character of correlated Chern insulators. Continuum model calculations reveal that Ising spin-orbit coupling dominates at Φ ≈ 0°, giving rise to flat bands with finite valley Chern numbers, whereas Rashba coupling dominates at larger Φ, resulting in topologically trivial bands. Transport measurements at quarter filling confirm this picture: Φ ≈ 0° devices exhibit C = +1 Chern insulators, consistent with spontaneous isospin polarization, whereas Φ ≈ 15° devices show C = 0 despite exhibiting similar correlated insulating behavior. The sharp contrast establishes crystallographic alignment as an additional tuning knob, complementary to twist angle, displacement field, and carrier density, for engineering correlated topological states in van der Waals heterostructures. Here, the authors show that in chiral twisted double bilayer graphene proximitized by WSe2, the crystallographic alignment angle switches a correlated insulating state between a Chern insulator and a trivial state, providing a tunable handle on flat-band topology.