Polarization analysis of excitons in monolayer and bilayer transition-metal dichalcogenides
Polarization analysis of excitons in monolayer and bilayer transition-metal dichalcogenides
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DOI：
10.1103/physrevb.92.125431
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发表时间：
2015-09-23
影响因子：
3.7
通讯作者：
Song, Yang
中科院分区：
文献类型：
--
作者：
Dery, Hanan;Song, Yang
单层和双层过渡金属二硫属化物中光学跃迁的偏振分析提供了有关自旋和谷（赝自旋）自由度的宝贵信息。为了解释给定单层过渡金属二硫属化物的光学性质，应该考虑（i）其自旋分裂导带的顺序，（ii）间散射是否容易出现声子瓶颈，（iii）以及是否可以通过电子空穴交换发生谷混合。利用这些原理，我们提出了一致的物理图片，阐明了这些材料的光谱中的各种特征。我们解释了单层 MoSe2 和单层 WSe2 中光学跃迁之间的差异，发现后者中的间接激子对应于迄今为止归因于与杂质结合的激子的几个低能光学跃迁。讨论了一种可以解释 MoSe2 极化消失的可能机制。最后，我们考虑了面外电场的影响，表明它可以由于与暗激子的 Rashba 型耦合而降低亮激子的初始极化。
The polarization analysis of optical transitions in monolayer and bilayer transition-metal dichalcogenides provides invaluable information on the spin and valley (pseudospin) degrees of freedom. To explain optical properties of a given monolayer transition-metal dichalcogenide, one should consider (i) the order of its spin-split conduction bands, (ii) whether intervalley scattering is prone to phonon bottleneck, (iii) and whether valley mixing by electron-hole exchange can take place. Using these principles, we present a consistent physical picture that elucidates a variety of features in the optical spectra of these materials. We explain the differences between optical transitions in monolayer MoSe2 and monolayer WSe2, finding that indirect excitons in the latter correspond to several low-energy optical transitions that so far were attributed to excitons bound to impurities. A possible mechanism that can explain the vanishing polarization in MoSe2 is discussed. Finally, we consider the effect of an out-of-plane electric field, showing that it can reduce the initial polarization of bright excitons due to a Rashba-type coupling with dark excitons.