Near Band‐Edge Optical Excitation Leading to Catastrophic Ionization and Electron–Hole Liquid in Room‐Temperature Monolayer MoS 2
Near Band‐Edge Optical Excitation Leading to Catastrophic Ionization and Electron–Hole Liquid in Room‐Temperature Monolayer MoS 2
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近带边光学激发导致灾难性电离和室温单层 MoS 2 中的电子空穴液体
DOI：
10.1002/pssb.201900223
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Gundogdu, Kenan
中科院分区：
文献类型：
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作者：
Younts, Robert;Bataller, Alexander;Ardekani, Hossein;Yu, Yiling;Cao, Linyou;Gundogdu, Kenan
原子薄材料表现出奇异的电学和光学特性。在简约的介电环境中，强烈的多体相互作用导致电子相的出现，从而极大地改变了导电性和光学响应。例如，这些多体相互作用可能导致集体态的形成，如Mott金属-绝缘体转变，电子-空穴液体和等离子体，以及激子凝聚，这些通常发生在低温和高激发密度下。本文证明了在单层MoS_2中，在室温下，用连续波(CW)在带隙以下激发形成了低密度(1010 cm−_2)激子气体。激发通量略有增加，就会触发纳秒相变，进入高密度电子-空穴液态，载流子密度增加三个数量级。研究表明，当材料在阈值注量下与CW激发处于平衡状态时，热机械膨胀和带隙的连续重整化导致光学吸收的突然增加，从而引发激子失控电离和高密度电子-空穴等离子体的形成。这种激发密度和载流子布居的突变可以为基于2D材料的前所未有的应用奠定基础。
Atomically thin materials exhibit exotic electronic and optical properties. Strong many‐body interactions from the reduced dielectric environment lead to electronic phases that drastically change conductivity and optical response. For example, these many‐body interactions can give rise to the formation of collective states such as Mott metal–insulator transitions, electron–hole liquids and plasmas, and excitonic condensates, which typically occur at cryogenic temperatures and high excitation densities. Herein, it is demonstrated that in monolayer MoS2at room temperature, a low‐density (1010cm−2) excitonic gas is formed with continuous wave (CW) below‐gap optical excitation. A slight increase in the excitation fluence triggers a nanosecond phase transition into a dense electron–hole liquid state with three orders of magnitude higher carrier density. This investigation suggests that while the material is in equilibrium with the CW excitation at the threshold fluence, thermomechanical expansion combined with continuous renormalization of the band gap leads to a sudden increase of optical absorption, which initiates runaway exciton ionization and the formation of a high density electron–hole plasma. Such abrupt changes in the excitation density and carrier population can be the basis of unprecedented applications based on 2D materials.