4.8 Article

Momentum-Dependent Oscillator Strength Crossover of Excitons and Plasmons in Two- Dimensional PtSe2

期刊

ACS NANO
卷 16, 期 8, 页码 12328-12337

出版社

AMER CHEMICAL SOC
DOI: 10.1021/acsnano.2c03322

关键词

monolayer PtSe2; momentum resolved electron energy loss spectroscopy; plasmons; excitons; 2D materials; electronic screening in 2D; ab initio calculations

资金

  1. JST-CREST [JPMJCR20B1, JPMJCR20B5, JPMJCR1993]
  2. JSPS-KAKENHI [JP16H06333, JP19K04434, JP17H04797]
  3. National Natural Science Foundation of China [51972204]
  4. Danish National Research Foundation [DNRF103]
  5. European Research Council (ERC) under the European Union [773122, 951215]
  6. VILLUM FONDEN [37789]
  7. A3 Foresight program
  8. European Research Council (ERC) [951215] Funding Source: European Research Council (ERC)

向作者/读者索取更多资源

The 1T-phase layered PtX2 chalcogenide has attracted attention due to its thickness dependent metal-semiconductor transition. By combining first-principles calculations with momentum resolved electron energy loss spectroscopy, the researchers studied collective excitations in 1T-PtSe2 and found that excitations in monolayer PtSe2 are mainly of excitonic nature.
The 1T-phase layered PtX2 chalcogenide 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. The qualitatively different momentum dependence of excitons and plasmons enables us to unambiguously disentangle their spectral fingerprints in the excited state spectrum of layered 1T-PtSe2. This will help to discern the charge carrier plasmon and locally map the optical conductivity and trace the layer-dependent semiconductor to metal transition in 1T-PtSe2 and other 2D materials.

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