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 ${\mathrm{WSe}}₂$ 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.