Metallic transition metal dichalcogenides like tantalum diselenide (TaSe₂) exhibit exciting behaviors at low temperatures, including the emergence of charge density wave (CDW) states. In this work, density functional theory (DFT) is used to catalog influences of van der Waals interactions and reduced dimensionality on the CDW atomic structures as a function of thickness, with the former effect being most strongly present between the layers of bulk TaSe₂, slightly reduced in few-layer TaSe₂, and effectively absent in monolayer (1L) TaSe₂. To support the validity of the DFT models, experimental Raman data are provided for monolayer, bilayer, and bulk TaSe₂ in the spectral range 165–215 cm⁻¹. The phonons seen in the experimental Raman spectra are compared with the results calculated from the DFT models as a function of temperature and layer number. The matching of data and calculations substantiates the model's description of the CDW structural formation as a function of thickness, which is shown in depth for 1L through 6L systems. These results highlight the importance of understanding interlayer interactions, which are pervasive in many quantum phenomena involving 2D confinement.

中文翻译：

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维数对2H-TaSe2电荷密度波相位的影响

金属过渡金属二硫化物，如二硒化钽 (TaSe ₂ ) 在低温下表现出令人兴奋的行为，包括电荷密度波 (CDW) 态的出现。在这项工作中，密度泛函理论 (DFT) 用于将范德华相互作用和降维对 CDW 原子结构的影响分类为厚度的函数，前者的影响在块状 TaSe ₂层之间最为强烈，在几层TaSe ₂中略有减少，而在单层（1L）TaSe ₂中有效地不存在。为了支持 DFT 模型的有效性，提供了光谱范围为 165–215 cm ^-1的单层、双层和块状 TaSe _{2的实验拉曼数据}. 将实验拉曼光谱中看到的声子与从 DFT 模型计算的结果作为温度和层数的函数进行比较。数据和计算的匹配证实了模型对 CDW 结构形成作为厚度函数的描述，这在 1L 到 6L 系统的深度显示。这些结果突出了理解层间相互作用的重要性，这种相互作用在许多涉及二维限制的量子现象中普遍存在。