Direction tunable singly polarized excitons in wurtzite monolayer

The optical response with tunable direction and carrier transport are highly desirable for optoelectronic devices. Here, we find a switchable direction dependent singly polarized exciton with E∥x or E∥y mode in the wurtzite (wz) monolayer by the ferroelastic phase transition or external strain. This reversible singly polarized switching is facilitated by valence band inversion, which arises from the reordering of heavy-hole and light-hole states around the valence band maximum in the wz monolayer. Our results facilitate precise modulation of polarized optical transition in two-dimensional materials and paves the way for designing optoelectronic devices with fully controllable polarization transition.