heterostructures*

Semiconducting van der Waals heterostructures represent an exceptionally interesting platform to study electronic many-body phenomena. The combination of structural complexity from crystallographic alignment with strong Coulomb interactions leads to drastic changes in the electronic structure challenging the description of the optical excitations, predominantly governed by excitons. To develop better fundamental understanding in our study we address the nature of exciton propagation in gate-tunable field-effect devices based on hBN-encapsulated WSe₂/MoSe₂ heterobilayers in the moiré-free limit of atomically reconstructed domains. Employing transient microscopy, we demonstrate efficient and gate-dependent exciton diffusion. Our results challenge the more common expectation of exciton localization at low densities and provide a solid basis to understand increasingly complex excitonic phenomena in these systems.