Phonon-Mediated Intervalley Relaxation Of Positive Trions In Monolayer Wse2

The valley relaxation mechanism of the bright state of positively charged excitons (bright positive trions) in monolayer (1L-) WSe2 is studied through polarization- and time-resolved photoluminescence and transient reflection measurements. A long valley relaxation time, exceeding 100 ps, is observed for positive trions at low temperature, which is notably prolonged when compared with the characteristic excitonic valley relaxation time of 10 ps. With increasing temperature, the relaxation time decreases to a few ps. This finding implies that phonon-mediated intervalley scattering is important for the relaxation process of the valley-polarized bright state of positive trions.