We present temperature-dependent resonance Raman measurements on monolayer WS₂ for the temperature range 4–295 K using excitation photon energies from 1.9 to 2.15 eV in ∼7 meV steps. These are analyzed to determine the resonance profiles of five previously assigned phonon based Raman peaks (A₁′, E′, 2ZA, LA, 2LA) and a previously unassigned peak at 485 cm^–1 whose possible attributions are discussed. The resonance profiles obtained are fitted to a perturbation theory derived model and it is shown that both excitons and trions are required to explain the profiles. The model is used to separate the contribution of exciton–exciton, trion–trion, and exciton–trion scattering to each of the Raman peaks at 4 K. This separation allows the ratios of the rates of scattering involving the A₁′ and E′ phonons for each of the three types of scattering to be determined. The explanation of the multiphonon Raman peaks requires the coupling of bright excitons and trions to large wavevector dark states. The fitting of the resonance Raman profiles for these Raman peaks demonstrates scattering of bright excitons to bright trions via these large wavevector dark states.

中文翻译：

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使用共振拉曼光谱法探测单层WS _2中的激子，三重子和暗激子

我们介绍了在温度为4–295 K的单层WS _2上，以1.9至2.15 eV的激发光子能量（约7 meV步长）在温度2–295 K上与温度有关的共振拉曼测量。分析这些信号以确定五个先前分配的基于声子的拉曼峰（A ₁ '，E'，2ZA，LA，2LA）和一个在485 cm ^–1处先前未分配的峰的共振曲线。讨论了其可能的归因。将获得的共振曲线拟合到微扰理论导出的模型，结果表明，需要激子和三重子来解释该曲线。该模型用于分离激子-激子，三重子-三重子和激子-三重子散射对4 K处每个拉曼峰的贡献。这种分离允许涉及A ₁ '和E'的散射速率之比确定三种散射类型中的每一种的声子。对多声子拉曼峰的解释要求将明亮的激子和三极子耦合到大的波矢暗态。这些拉曼峰的共振拉曼轮廓的拟合表明，通过这些大波矢暗态，明亮的激子向明亮的三子散射。