Fine structure mediated magnetic response of trion valley polarization in monolayer WSe2

We construct a valley dynamics model, involving both bright and dark excitonic states, to determine magneto optical properties of excitons and singlet and triplet trions (charged excitons), in monolayer WSe2 subjected to magnetic fields. Our computed excitonic peak energy and valley Zeeman splitting, which are essential for the magnetic-field-associated valley dynamics, in great agreement with experimental data by Lyons et al. [Nat. Commun. 10, 2330 (2019)]. In addition, we find that the valley polarizations of excitons and trions respectively exhibit the "X"-and "V"-shape dependence on magnetic field, consistent with experimental measurements by Aivazian et al. [Nat. Phys. 11, 148 (2015)]. Remarkably, beyond available experimental measurements, our theory predicts an X-V shape conversion and even a new paradigm more than the X and V shapes, which depend on the trion fine structure arising from exchange interactions and involving a magnetic swap of ground states between singlet and triplet trions. Our results are helpful for elucidating recent experimental data about the valley-degeneracy-lifting-mediated valley dynamics of different trion species and should stimulate experiments probing relevant new magneto-optical features.