Interlayer exciton laser of extended spatial coherence in atomically thin heterostructures.

Two-dimensional semiconductors have emerged as a new class of materials for nanophotonics owing to their strong exciton-photon interaction ^1,2 and their ability to be engineered and integrated into devices ³ . Here we take advantage of these properties to engineer an efficient lasing medium based on direct-bandgap interlayer excitons in rotationally aligned atomically thin heterostructures ⁴ . Lasing is measured from a transition-metal dichalcogenide heterobilayer (WSe ₂ -MoSe ₂ ) integrated in a silicon nitride grating resonator. An abrupt increase in the spatial coherence of the emission is observed across the lasing threshold. The work establishes interlayer excitons in two-dimensional heterostructures as a gain medium with spatially coherent lasing emission and potential for heterogeneous integration. With electrically tunable exciton-photon interaction strengths ⁵ and long-range dipolar interactions, these interlayer excitons are promising for application as low-power, ultrafast lasers and modulators and for the study of many-body quantum phenomena ⁶ .