Ascertain the mechanism of negative valley polarization in brightened dark excitonic complexes in monolayer WSe2

Ascertain the precise physical mechanism that yields a negative degree of circular polarization in the photoluminescence of brightened dark excitonic complexes (gray excitons and trions) in monolayer WSe2 under magnetic-field brightening, beyond speculative explanations involving relaxation of bright excitons to dark excitons through intervalley electron scattering.

Background

The authors observe a negative degree of circular polarization at the semi-dark trion energy in WS2 and note similar phenomena reported previously in WSe2 under magnetic-field brightening. In the WSe2 experiments, the negative polarization of brightened dark excitonic complexes was established, but its underlying mechanism was not conclusively determined.

Understanding this mechanism is crucial for controlling valley polarization in TMD materials and for developing valleytronic applications. A definitive explanation would clarify the roles of intervalley scattering, spin-dependent processes, and exciton–trion interconversions in producing the observed polarization reversal.