Brightening Spin-Forbidden Dark Excitons in Transition-Metal Dichalcogenides by Antiferromagnetic Magnons

Abstract

Dark excitons in atomically thin van der Waals materials, with their long lifetimes, are appealing candidates for quantum information processing and storage. Their charge-neutral nature makes optical readout and control essential, due to the restriction on electrical probing, yet their spin-forbidden character prevents direct coupling to light. Angular momentum transfer between quasiparticles provides a promising route to overcome this limitation. Here, we fabricate a hybrid heterostructure incorporating an antiferromagnetic layered semiconductor CrSBr and transition-metal dichalcogenides. Below the Néel temperature, we observe the brightened dark exciton emission from monolayer MoSe2 in the photoluminescence spectra located at 51 meV below the optically inactive states. This energy difference coincides with the magnon energy of CrSBr. Moreover, the energy difference varying with the magnetic field matches the magnon g-factor, and its temperature dependence is consistent with magnon’s thermal evolution. According to the indicative results that correlate the brightened dark exciton with the magnon, we propose that the dark-to-bright conversion is enabled by interfacial coupling between the magnetic dipole moment of the magnon and the antiparallel spin texture of the dark exciton. This mechanism is well demonstrated by the valley-contrast experiment. Our work establishes a general and easy-to-implement approach to manipulate dark excitons and explore exciton physics in two-dimensional materials without complex device architectures or high magnetic fields, advancing exciton-based and magnon-mediated quantum devices.