Broadband transient THz conductivity of the transition-metal dichalcogenide MoS2
Broadband transient THz conductivity of the transition-metal dichalcogenide MoS2
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DOI：
10.1117/12.2080748
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
J. H. Buss;Ryan P. Smith;G. Coslovich;R. Kaindl
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文献类型：
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作者：
J. H. Buss;Ryan P. Smith;G. Coslovich;R. Kaindl
过渡金属二卤化物的瞬时动力学对于阐明纳米尺度上的基本多粒子相互作用以及新的应用具有重要的意义。我们报道了对片状半导体MoS_2的超快太赫兹研究，以获得这种多层母体化合物中光激发的间接e-h对的非平衡电导。当平衡输运是类Drude时，近红外光激发产生了由两个组分组成的复杂的光致电导。在2太赫兹以下，移动载流子在低频响应中占主导地位，而在低温下观察到额外的过剩电导率，在4太赫兹附近增强。动力学中出现了两个时间尺度：由于非辐射复合而产生的慢ns弛豫，以及与高频太赫兹特征有关的较快的低于100ps的衰减。我们讨论了MoS2中激子内跃迁模型中的宽THz峰。它很好地符合预期的结合能和振子强度，但导致需要电子不均匀相的激子部分的反常温度依赖关系。
The transient dynamics of transition-metal dichalcogenides is of significant interest for clarifying fundamental manyparticle interactions at the nanoscale as well as for novel applications. We report an ultrafast terahertz study up to 7 THz of the lamellar semiconductor MoS2 to access the non-equilibrium conductivity of photo-excited indirect e-h pairs in this multi-layered parent compound. While the equilibrium transport is Drude-like, near-IR optical excitation results in a complex photo-induced conductivity that consists of two components. Mobile charge carriers dominate the low frequency response below 2 THz, while at low temperatures an additional excess conductivity is observed that is enhanced around 4 THz. Two time scales appear in the dynamics: a slow ns relaxation due to non-radiative recombination and a faster sub-100 ps decay connected to the high-frequency THz feature. We discuss the broad THz peak within a model of intra-excitonic transitions in MoS2. It agrees well with the expected binding energy and oscillator strength, yet results in an anomalous temperature dependence of the exciton fraction requiring an electronically inhomogeneous phase.