Charting the Exciton-Polariton Landscape in WSe2 Thin Flakes by Cathodoluminescence Spectroscopy

TL;DR

This study uses cathodoluminescence spectroscopy to explore exciton-polariton phenomena in freestanding WSe2 flakes, revealing strong light-matter interactions and energy transfer dynamics that could inform future optoelectronic nanocircuits.

Contribution

It demonstrates the optical response and exciton-photon interactions in WSe2 nanocavities, highlighting the role of confinement effects at flake edges, with combined experimental and theoretical insights.

Findings

Observation of long-range propagating exciton-polaritons.

Direct imaging of energy transfer from cavity resonances.

Confinement effects at flake edges modulate exciton-photon coupling.

Abstract

Semiconducting transition-metal dichalcogenides (TMDCs) provide a fascinating discovery platform for strong light-matter interaction effects in the visible spectrum at ambient conditions. While most of the work has focused on hybridizing excitons with resonant photonic modes of external mirrors, cavities, or nanostructures, intriguingly, TMDC flakes of sub-wavelength thickness can themselves act as nanocavities. Here, we determine the optical response of such freestanding planar waveguides of WSe$_2$, by means of cathodoluminescence spectroscopy. We reveal strong exciton-photon interaction effects that foster long-range propagating exciton-polaritons and enable direct imaging of the energy transfer dynamics originating from cavity-like Fabry-Perot resonances. Furthermore, confinement effects due to discontinuities in the flakes are demonstrated as an efficient means to tailor the exciton-photon coupling strength, along the edges of natural flakes. Our combined experimental and theoretical results provide a deeper understanding of exciton-photon self-hybridization in semiconducting TMDCs and may pave the way to optoelectronic nanocircuits exploiting exciton-photon interaction.