Brightening dark excitons and trions in systems with a Mexican-hat energy dispersion: example of InSe

Monolayer InSe

InSe is a III–VI chalcogenide (metal-group III atom and group VI chalcogenide), with a hexagonal structure with unit vectors \({{\boldsymbol{a}}}_{1}=\left(a/2,\sqrt{3}a/2\right)\) and