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

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 works have focused on hybridizing excitons with resonant photonic modes of external mirrors, cavities, or nanostructures, intriguingly, TMDC flakes of subwavelength thickness can themselves act as nanocavities. Herein, the optical response of such freestanding planar waveguides of WSe2 by means of cathodoluminescence spectroscopy is determined. 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 are revealed. Furthermore, confinement effects due to discontinuities in the flakes are demonstrated as an efficient means to tailor mode energies, spin-momentum couplings, and the exciton-photon coupling strength, as well as to promote photon-mediated exciton-exciton interactions. The 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 beyond the routinely employed two-oscillator coupling effects.

Automated summary

This study determines the optical response of WSe2 flakes using cathodoluminescence spectroscopy and reveals strong exciton-photon interaction effects and energy transfer dynamics. Furthermore, confinement effects due to discontinuities in the flakes are demonstrated and used to tailor mode energies, spin-momentum couplings, and exciton-photon coupling strength, as well as to promote photon-mediated exciton-exciton interactions.