Interactions and ultrafast dynamics of exciton complexes in a monolayer semiconductor with electron gas

The experimental/theoretical data presented is related to the article "Interactions and ultrafast dynamics of exciton complexes in a monolayer semiconductor with electron gas"We present femtosecond pump-probe measurements of neutral and charged exciton optical response in monolayer MoSe2 to resonant photoexcitation of a given exciton state in the presence of 2D electron gas. We show that creation of charged exciton (X−) population in a given K+, K− valley requires the capture of available free carriers in the opposite valley and reduces the interaction of neutral exciton (X) with the electron Fermi sea. We also observe spectral broadening of the X transition line with the increasing X− population caused by efficient scattering and excitation induced dephasing. From the valley-resolved analysis of the observed effects we are able to extract the spin-valley relaxation times of free carriers as a function of carrier density. Moreover, we analyze the oscillator strength and energy shift of X in the regime of interaction with electron Fermi sea under resonant excitation. From this we can observe the process of X decay by radiative recombination paired with trion formation. We demonstrate an increase of neutral exciton relaxation rate with the introduction of Fermi sea of electrons. We ascribe the observed effect to the increased efficiency of the trion formation, as well as the radiative decay caused by the screening of disorder by the free carriers.

本数据集所呈现的实验与理论数据，关联于题为"Interactions and ultrafast dynamics of exciton complexes in a monolayer semiconductor with electron gas"的研究论文。本研究针对存在二维电子气（2D electron gas）时特定激子态的共振光激发过程，开展了单层二硒化钼（MoSe₂）中中性激子（neutral exciton）与带电激子（charged exciton）光学响应的飞秒（femtosecond）泵浦探测（pump-probe）测量。我们发现，在特定K+、K−谷中构建带电激子（X−）布居，需要俘获反谷中的可用自由载流子，同时会削弱中性激子（X）与电子费米海（Fermi sea）之间的相互作用。我们还观测到，随着X−布居的增加，X跃迁谱线出现展宽，该现象源于高效散射与激发诱导的退相过程。通过对观测到的效应开展谷分辨分析，我们得以提取出自由载流子的自旋谷弛豫时间随载流子密度的变化关系。此外，我们还分析了共振激发条件下，处于与电子费米海相互作用区间的X的振子强度（oscillator strength）与能量位移。基于此，我们观测到了中性激子通过辐射复合并伴随负激子形成的衰变过程。我们证实，引入电子费米海后，中性激子的弛豫速率会提升。我们将观测到的这一现象归因于负激子形成效率的提升，以及自由载流子对无序效应的屏蔽所引发的辐射衰变过程。