Understanding of electron-phonon coupling (EPC) in two dimensional (2D) materials manifesting as phonon renormalization is essential to their possible applications in nanoelectronics. Here we report in-situ Raman measurements of electrochemically top-gated 2, 3 and 7 layered 2H-MoTe2channel based field-effect transistors (FETs). While the E12gand B2gphonon modes exhibit frequency softening and linewidth broadening with hole doping concentration (p) up to ∼ 2.3 ×1013/cm2, A1gmode shows relatively small frequency hardening and linewidth sharpening. The dependence of frequency renormalization of the E12gmode on the number of layers in these 2D crystals confirms that hole doping occurs primarily in the top two layers, in agreement with recent predictions. We present first-principles density functional theory (DFT) analysis of bilayer MoTe2that qualitatively captures our observations, and explain that a relatively stronger coupling of holes with E12gor B2gmodes as compared with the A1gmode originates from the in-plane orbital character and symmetry of the states at valence band maximum (VBM). The contrast between the manifestation of EPC in monolayer MoS2and those observed here in a few-layered MoTe2demonstrates the role of the symmetry of phonons and electronic states in determining the EPC in these isostructural systems.

中文翻译：

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几层 2H-MoTe2 晶体管中的对称性诱导声子重整化：拉曼和第一性原理研究

理解表现为声子重整化的二维 (2D) 材料中的电子-声子耦合 (EPC) 对于它们在纳米电子学中的可能应用至关重要。在这里，我们报告了基于电化学顶栅 2、3 和 7 层 2H-MoTe2 通道的场效应晶体管 (FET) 的原位拉曼测量。虽然 E12g 和 B2g 声子模式表现出频率软化和线宽加宽，空穴掺杂浓度 (p) 高达 ~ 2.3 ×1013/cm2，但 A1g 模式显示出相对较小的频率硬化和线宽锐化。E12gmode 的频率重整化对这些 2D 晶体层数的依赖性证实，空穴掺杂主要发生在顶部两层，与最近的预测一致。我们提出了双层 MoTe2 的第一性原理密度泛函理论 (DFT) 分析，它定性地捕捉了我们的观察结果，并解释了与 A1gmode 相比，E12gor B2gmodes 的空穴耦合相对更强源于面内轨道特征和状态的对称性在价带最大值 (VBM)。EPC 在单层 MoS2 中的表现与此处在几层 MoTe2 中观察到的对比证明了声子和电子态的对称性在确定这些同构系统中的 EPC 中的作用。