Excitonic order tuned by electric fields and driven by interorbital Coulomb interactions in twisted bilayer graphene

Excitonic order, as a representative electronic instability in strongly correlated systems, has attracted significant attention in moiré systems. In this work, we investigate the emergence and tunability of excitonic order in twisted bilayer graphene within an effective two-orbital Hubbard model, using large-scale constrained-path quantum Monte Carlo simulations. We demonstrate that the excitonic correlations are significantly enhanced by the external electric field ε, the inter-orbital Coulomb interaction V ⊥ , and the inter-orbital hopping t ⊥ . By analyzing both short-range and long-range excitonic correlation functions across different lattice sizes, we find that long-range excitonic correlations are robust against finite-size effects and provide reliable evidence for excitonic condensation. Furthermore, we reveal a clear interplay between magnetic order and excitonic order. The spin structure factor shows that increasing ε, V ⊥ , and t ⊥ suppresses the antiferromagnetic order, indicating that excitonic order emerges as a competing instability with magnetism. Among these factors, the external electric field plays the dominant role in destabilizing antiferromagnetism and promoting excitonic correlations. Our results establish a unified physical picture in which excitonic order in twisted bilayer graphene can be effectively controlled by tuning interlayer coupling and external fields, providing a promising route for realizing excitonic condensation in strongly correlated moiré systems.