We investigate valley dynamics associated with trions in monolayer tungstendiselenide (WSe2) using polarization resolved two-color pump-probespectroscopy. When tuning the pump and probe energy across the trion resonance,distinct trion valley polarization dynamics are observed as a function ofenergy and attributed to the intra-valley and inter-valley trions in monolayerWSe2. We observe no decay of a near-unity valley polarization associated withthe intra-valley trions during ~ 25 ps, while the valley polarization of theinter-valley trions exhibits a fast decay of ~ 4 ps. Furthermore, we show thatresonant excitation is a prerequisite for observing the long-lived valleypolarization associated with the intra-valley trion. The exceptionally robustvalley polarization associated with resonantly created intra-valley trionsdiscovered here may be explored for future valleytronic applications such asvalley Hall effects.
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