Monolayer transition metal dichalcogenides (TMDs) have been in focus of current research, among others due to their remarkable exciton landscape consisting of bright and dark excitonic states. Although dark excitons are not directly visible in optical spectra, they have a large impact on exciton dynamics and hence their understanding is crucial for potential TMD-based applications. Here, we study brightening mechanisms of dark excitons via interaction with phonons and in-plane magnetic fields. We show clear signatures of momentum- and spin-dark excitons in WS 2 , WSe 2 and MoS 2 , while the photoluminescence of MoSe 2 is only determined by the bright exciton. In particular, we reveal the mechanism behind the brightening of states that are both spin- and momentum-dark in MoS 2 . Our results are in good agreement with recent experiments and contribute to a better microscopic understanding of the exciton landscape in TMDs.

中文翻译：

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过渡金属二卤化物中自旋和动量暗激子的增亮

单层过渡金属二硫化碳（TMD）一直是当前研究的重点，这是由于它们具有由亮和暗激子态组成的非凡激子态。尽管暗激子在光谱中不直接可见，但它们对激子动力学有很大影响，因此，它们的理解对于潜在的基于TMD的应用至关重要。在这里，我们通过与声子和面内磁场的相互作用研究暗激子的增亮机理。我们在WS 2，WSe 2和MoS 2中显示出动量和自旋暗激子的清晰特征，而MoSe 2的光致发光仅由明亮的激子决定。特别是，我们揭示了MoS 2中处于自旋和动量暗状态的状态变亮的背后机制。