Valley dynamics of different trion species in monolayer WSe2
Valley dynamics of different trion species in monolayer WSe2
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单层WSe2中不同三重体物种的谷动力学
DOI：
10.1063/1.5112823
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发表时间：
2019-08-19
影响因子：
4
通讯作者：
Qu, Fanyao
中科院分区：
文献类型：
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作者：
Fu, Jiyong;Cruz, Junio M. R.;Qu, Fanyao
我们建立了一个模型，考虑光学非活性的激子暗态，包括自旋禁止和动量禁止类型，以探索单层WSe2中不同三种离子的谷动力学。我们观察到两种不同的状态，由两种典型的明暗散射过程决定，即自旋翻转和自旋守恒。当自旋翻转散射与自旋守恒散射相当时，我们发现所有激子态（包括激子、单重态和三重态）的谷极化（VPs）相对于激发激光都是共极化的，这与现有的实验测量结果一致。有趣的是，当自旋守恒散射优于自旋翻转散射时，我们观察到单重态trion的VP反转。这种迷人的谷控制打开了设想中的谷场效应晶体管（FET）（自旋场效应晶体管的模拟物）的大门。此外，我们发现反向VP在趋于稳定之前会不断增强，这为相干控制谷伪自旋提供了一个有希望的平台。我们的发现应该刺激实验探索VP反转的样品具有强自旋守恒散射。
We develop a model, taking into account optically inactive excitonic dark states, of both spin-forbidden and momentum-forbidden types, to explore valley dynamics of different trion species in monolayer WSe2. We observe two distinct regimes, determined by two typical bright-dark scattering processes, i.e., the spin-flip and spin-conserving ones. When the spin-flip scattering is comparable to the spin-conserving one, we find that the valley polarizations (VPs) of all excitonic states including excitons and singlet and triplet trions are copolarized with respect to the excitation laser, consistent with available experimental measurements. Interestingly, when the spin-conserving scattering dominates over the spin-flip one, we observe the reversal of VP of the singlet trion. This fascinating valley control opens the door to an envisaged valley field-effect transistor (FET) (an analog of spin FET). Furthermore, we reveal that the reversed VP strengthens until it becomes stabilized, offering a promising platform for coherent control of valley pseudospin. Our findings should stimulate experiments probing the VP reversal in samples with strong spin-conserving scattering.