Long-Lived Valley Polarization of Intravalley Trions in Monolayer WSe2

We investigate valley dynamics associated with trions in monolayer tungsten diselenide (WSe2) using polarization resolved two-color pump-probe spectroscopy. When tuning the pump and probe energy across the trion resonance, distinct trion valley polarization dynamics are observed as a function of energy and attributed to the intravalley and intervalley trions in monolayer WSe2. We observe no decay of a near-unity valley polarization associated with the intravalley trions during similar to 25 ps, while the valley polarization of the intervalley trions exhibits a fast decay of similar to 4 ps. Furthermore, we show that resonant excitation is a prerequisite for observing the long-lived valley polarization associated with the intravalley trion. The exceptionally robust valley polarization associated with resonantly created intravalley trions discovered here may be explored for future valleytronic applications such as valley Hall effects.