Probing excitons in transition metal dichalcogenides by Drude-like exciton intraband absorption†,Nanoscale

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Probing excitons in transition metal dichalcogenides by Drude-like exciton intraband absorption†
Nanoscale ( IF 5.8 ) Pub Date : 2018-04-19 00:00:00 , DOI: 10.1039/c8nr03135e
Siqi Zhao _{1,

2,

3,

4,

5} , Dawei He _{1,

2,

3,

4,

5} , Jiaqi He _{1,

2,

3,

4,

5} , Xinwu Zhang _{1,

2,

3,

4,

5} , Lixin Yi _{1,

2,

3,

4,

5} , Yongsheng Wang _{1,

2,

3,

4,

5} , Hui Zhao _{6,

7,

8,

9}

Affiliation

Understanding excitonic dynamics in two-dimensional semiconducting transition metal dichalcogenides is important for developing their optoelectronic applications. Recently, transient absorption techniques based on resonant excitonic absorption have been used to study various aspects of excitonic dynamics in these materials. The transient absorption in such measurements originates from phase-space state filling, bandgap renormalization, or screening effects. Here we report a new method to probe excitonic dynamics based on exciton intraband absorption. In this Drude-like process, probe photons are absorbed by excitons in their intraband excitation to higher energy states, causing a transient absorption signal. Although the magnitude of the transient absorption is lower than that of the resonant techniques, the new method is less restrictive on the selection of probe wavelength, has a larger linear range, and can provide complementary information on photocarrier dynamics. Using the WS₂ monolayer and bulk samples as examples, we show that the new method can probe exciton–exciton annihilation at high densities and reveal exciton formation processes. We also found that the exciton intraband absorption cross section of the WS₂ monolayer is on the order of 10⁻¹⁸ cm².

中文翻译：

通过类Drude激子带内吸收来探测过渡金属二卤化物中的激子†

理解二维半导体过渡金属二卤化物中的激子动力学对于开发其光电应用很重要。最近，基于共振激子吸收的瞬态吸收技术已被用于研究这些材料中激子动力学的各个方面。此类测量中的瞬态吸收源自相空间状态填充，带隙重归一化或屏蔽效应。在这里，我们报告了一种基于激子带内吸收来探测激子动力学的新方法。在这种类似Drude的过程中，探针光子在其带内激发中被激子吸收到更高的能量状态，从而产生瞬态吸收信号。尽管瞬态吸收的幅度低于共振技术，该新方法对探针波长的选择限制较少，具有较大的线性范围，并且可以提供有关光电载流子动力学的补充信息。使用WS_以2个单层和大量样品为例，我们证明了该新方法可以探测高密度下的激子-激子ni灭，并揭示了激子的形成过程。我们还发现，WS₂单层的激子带内吸收截面约为10^-18 cm²。

更新日期：2018-04-19

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