Long-Lived Valley Polarization of Intra-Valley 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 intra-valley and inter-valley trions in monolayer WSe2. We observe no decay of a near-unity valley polarization associated with the intra-valley trions during ~ 25 ps, while the valley polarization of the inter-valley trions exhibits a fast decay of ~ 4 ps. Furthermore, we show that resonant excitation is a prerequisite for observing the long-lived valley polarization associated with the intra-valley trion. The exceptionally robust valley polarization associated with resonantly created intra-valley trions discovered here may be explored for future valleytronic applications such as valley Hall effects. 
Akshay Singh, Kha Tran, Mirco Kolarczik, Joe Seifert, Yiping Wang, Kai   Hao, Dennis Pleskot, Nathaniel M. Gabor, Sophia Hel...
cond-mat.mes-hall