Coulomb engineering of exciton broadening in monolayer transition metal dichalcogenides

Understanding and controlling spectral broadening is the core of optoelectronic applications. Monolayer transition metal dichalcogenides (TMDs) intrinsically have large homogeneous exciton linewidth due to rapid exciton decay, but it is often masked by inhomogeneous spectral broadening. It is effective to construct van der Waals heterostructures (vdWhs) with atomically clean interfaces helps to reduce the spectral disorder. In particular, hexagonal boron nitride (hBN) encapsulation serves as a flat protective layer that mitigates inhomogeneous exciton broadening, while graphene capping allows only neutral exciton emission through fast interlayer charge transfer. Based on these disorder-minimized vdWhs, we propose a novel approach to control the homogeneous exciton linewidth in MoSe₂ monolayers by Coulomb engineering. Introducing graphene on monolayer molybdenum disulfide (MoSe₂) with hBN encapsulation layer increases the homogeneous exciton linewidth, while simultaneously reducing inhomogeneous broadening. Subsequently, placing additional an layer on the graphene/MoSe₂ heterostructures weakens the Coulomb interactions, resulting in decreased homogeneous exciton linewidth. By precisely controlling the Coulomb interaction, this approach provides a promising platform to elucidate the exciton broadening dynamics of monolayer TMDs in a controlled manner.