Strongly Bound Charge-Transfer Interface Excitons in Lateral Monolayer MoSe₂-WSe₂ Heterostructures

In lateral heterostructures of two different transition-metal dichalcogenide monolayers with type-II band alignment, appropriately engineered interface widths and band offsets give rise to dipolar charge-transfer interface excitons, characterized by electrons and holes localized on opposite sides of the junction. This topic has been little explored, mainly because of difficulties to synthesize clean and uniform lateral interfaces. Here, using different experimental techniques, we systematically probe excitons in lateral monolayer MoSe₂-WSe₂ heterostructures with both sharp and diffuse junctions. Using low-temperature photoluminescence spectroscopy, we find an additional spectral signal exclusively at sharp junctions, compatible with a dipolar charge-transfer exciton. Parameter-free ab initio many-body perturbation theory yields stable, strongly bound dipolar charge-transfer excitons at the lateral MoSe₂-WSe₂ interface already for small lateral band offsets, supporting the assignment of our detected photoluminescence signal at sharp junctions to a dipolar charge-transfer interface exciton.