Valley Zeeman Splitting-Enhanced Spin-Forbidden Dark Exciton Formation in Magnetically V-Doped WSe2 Monolayer and WSe2/MoSe2 Heterostructure.

Spin-forbidden dark excitons are promising for optoelectronic devices due to the significantly extended lifetimes. Although their formation mechanism in monolayer MoS2 has been theoretically revealed, time-reversal symmetry intrinsically protects valley degeneracy, imposing a fundamental limit on the formation efficiency. However, effective strategies to overcome this limitation remain unclear. Here, the photoexcitation and relaxation dynamics in the WSe2 monolayer and WSe2/MoSe2 heterostructure are investigated through nonadiabatic molecular dynamics combined with light-matter interaction and the GW plus real-time Bethe-Salpeter equation. We discover that although many-body interactions, including electron-phonon coupling, electron-hole Coulomb and exchange interactions, and spin-orbit interaction, synergistically drive spin-forbidden dark exciton formation, inherent valley degeneracy restricts the formation efficiency to ∼50%. To overcome this limitation, magnetic vanadium doping is introduced to induce an internal magnetic exchange field that breaks time-reversal symmetry, causing a massive valley Zeeman splitting (>100 meV). This effectively suppresses the competing exciton relaxation channels, enhancing the spin-forbidden dark exciton generation efficiency to 98% in the WSe2 monolayer and 85% in the WSe2/MoSe2 heterostructure. This intrinsic magnetic doping strategy is crucial for lifting valley degeneracy and enhancing spin-forbidden dark exciton formation, providing a foundation for optoelectronic devices based on long-lived dark excitons.