Ultrafast Exciton and Trion Dynamics in High-Quality Encapsulated MoS 2 Monolayers
Ultrafast Exciton and Trion Dynamics in High-Quality Encapsulated MoS 2 Monolayers
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高质量封装 MoS 2 单层膜中的超快激子和 Trion 动力学
DOI：
10.1002/pssb.202200376
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Genco A
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文献类型：
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作者：
Genco A
单层过渡金属二硫属化物（TMD）中的极端限制和减少的屏蔽导致出现紧密束缚的激子，由于强库仑相互作用，这些激子也可以与自由电荷耦合，形成三重子。低温和封装在六方氮化硼（hBN）中可以缩小激子线宽，接近均匀展宽的状态，主要由辐射衰变主导。超快光谱是研究 TMD 单层中激子形成和弛豫动力学的完美工具。然而，高质量六方氮化硼封装结构的横向尺寸通常为几微米，因此需要在泵浦探针实验中结合高空间和时间分辨率。在此，使用定制的宽带泵浦探针光学显微镜在8 K下测量高质量六方氮化硼封装的单层MoS2中中性和带电激子的超快动力学。中性激子表现出7.5 meV的窄线宽，接近均匀极限，这与泵浦探针测量的约130 fs的快速复合时间有关。此外，观察到三离子与中性三离子的动力学显着不同。这些结果为TMD单层中激子复合过程提供了新的见解，为探索TMD异质结构中激子及其多体复合物的超快行为铺平了道路。
The extreme confinement and reduced screening in monolayer transition metal dichalcogenides (TMDs) leads to the appearance of tightly bound excitons which can also couple to free charges, forming trions, owing to strong Coulomb interactions. Low temperatures and encapsulation in hexagonal boron nitride (hBN) can narrow the excitonic linewidth, approaching the regime of homogeneous broadening, mostly dominated by the radiative decay. Ultrafast spectroscopy is a perfect tool to study exciton formation and relaxation dynamics in TMD monolayers. However, high‐quality hBN‐encapsulated structures have usually lateral sizes of the order of a few micrometers, calling for the combination of high spatial and temporal resolution in pump–probe experiments. Herein, a custom broadband pump–probe optical microscope is used to measure the ultrafast dynamics of neutral and charged excitons in high‐quality hBN‐encapsulated monolayer MoS2at 8 K. Neutral excitons exhibit a narrow linewidth of 7.5 meV, approaching the homogeneous limit, which is related to the fast recombination time of ≈130 fs measured in pump–probe. Moreover, markedly different dynamics of the trions over the neutral ones are observed. The results provide novel insights on the exciton recombination processes in TMD monolayers, paving the way for exploring the ultrafast behavior of excitons and their many‐body complexes in TMD heterostructures.