Probing exciton-plasmon interaction by scanning electron beam
Fatemeh Davoodi a, Nahid Talebi a
a Institute for Experimental and Applied Physics, Kiel University, 24118 Kiel, Germany
Proceedings of Electron Beam Spectroscopy for Nanooptics 2021 (EBSN2021)
Online, Spain, 2021 June 14th - 15th
Organizers: Mathieu Kociak and Nahid Talebi
Poster, Fatemeh Davoodi, 041
Publication date: 8th June 2021

Here, the interactions between excitons and surface plasmon polaritons in Au-WSe2-Au multilayered structure composed of gold and WSe2 are investigated analytically using a transfer-matrix method, within the context of electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) spectroscopy. We thoroughly analyzed the excitation of optical exciton-polaritons and surface exciton-polariton in Au-WSe2-Au structures by a swift electron with the charge of q and the velocity of υ=zυe. The CL spectra is modeled using the Poynting theorem. Regarding the energy-loss spectra, the induced electric-field component Ezind along the electron trajectory is calculated and inserted inside the energy-loss probability [1]. When an electron travels through the multilayer structure, it couples to both excitons and plasmons of the structure. Because the photons remain trapped at the dielectric-air interface, the created Cherenkov radiation is captured inside the waveguide due to the Fabry-Pérot resonances [2]. In addition, we investigate the strong coupling effects between excitons and plasmons and the creation of hybrid polaritons (plexciton) [3]. When two gold layers are positioned at a certain distance with respect to each other, void plasmons are excited in the vacuum between the layers, which acts as a more efficient cavity configuration compare to the total internal reflection at the boundaries of a semiconductor waveguide such as a WSe2 thin film. Thus, placing a WSe2 in between two Au layers can result in a stronger exciton-photon interaction. A significant shift of the peaks in both CL and EELS spectra compared to the exciton A, exciton B, and the plasmon peaks highlights the influence of strong coupling effects on the resulting eigen energies of the system. The dispersion diagram of the new polariton modes manifested in the MREELS map demonstrates that in this configuration, exciton B can also strongly interact with photons. Our analytical results pave the way towards a better understanding of the parameters involved in strong exciton-plasmon couplings and lead us to design ultra-confined photonic cavity geometries enhancing the couplings between exciton-polaritons and SPPs.

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