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arXiv 2203.05088cond-mat.mtrl-scicond-mat.mes-hallquant-ph
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二维PtSe2中激子和等离子体激元的动量相关振子强度交叉

Momentum-dependent oscillator strength crossover of excitons and plasmons in two-dimensional PtSe2

Jinhua Hong, Mark Kamper Svendsen, Masanori Koshino, Thomas Pichler, Hua Xu, Kazu Suenaga, Kristian Sommer Thygesen

摘要:

1 T相层状PtX_2硫族化合物由于其厚度依赖的金属-半导体转变由强的层间耦合驱动而引起了广泛的兴趣。虽然这种典型材料系统的基态性质已被广泛探索,但其基本激发光谱仍然知之甚少。在这里,我们将第一性原理计算与动量(q)分辨电子能量损失谱(q-EELS)相结合,研究1 T-PtSe 2从单层极限到体相的集体激发。在有限的动量转移,所有的光谱是由两个不同的带间等离子体激元,分散到更高的能量与增加q。有趣的是,在二维(2D)限制的情况下,长距离屏蔽,抑制长波长等离子体的形成。因此,在小q限制下,单层PtSe 2中的激发仅具有激子性质,并且损耗谱与光谱一致。我们的工作揭示了层状1 T-PtSe 2的激发态光谱,并建立了二维材料中激子和等离子体激元的定性不同的动量依赖关系。

英文摘要:

The 1T-phase layered PtX2 chalcogenides has attracted widespread interest due to its thickness dependent metal-semiconductor transition driven by strong interlayer coupling. While the ground state properties of this paradigmatic material system have been widely explored, its fundamental excitation spectrum remains poorly understood. Here we combine first principles calculations with momentum (q) resolved electron energy loss spectroscopy (q-EELS) to study the collective excitations in 1T-PtSe2 from the monolayer limit to the bulk. At finite momentum transfer all the spectra are dominated by two distinct interband plasmons that disperse to higher energy with increasing q. Interestingly, the absence of long-range screening in the two-dimensional (2D) limit, inhibits the formation of long wavelength plasmons. Consequently, in the small-q limit, excitations in monolayer PtSe2 are exclusively of excitonic nature, and the loss spectrum coincides with the optical spectrum. Our work unravels the excited state spectrum of layered 1T-PtSe2 and establishes the qualitatively different momentum dependence of excitons and plasmons in 2D materials.

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