Dark excitations in monolayer transition metal dichalcogenides

To date, most studies on electronic excitations in 2D materials have focused on the optically active excitations, but recent experiments have highlighted the existence of dark states, which are equally important in many respects. Here, the authors use a00exb i00exn00exi00ext00exi00exo many-body calculations to unravel the nature of the dark excitations in monolayer MoSe₂, MoS₂, WSe₂, and WS₂. The lowest neutral and charged excitations are found to be dark. In accordance with experiment, dark trions are weaker bound than bright trions.