Visualizing plasmon-exciton polaritons at the nanoscale using electron microscopy

TL;DR

This paper demonstrates nanometer-scale visualization of plasmon-exciton polaritons, or plexcitons, using electron energy loss spectroscopy in a transmission electron microscope, revealing detailed coupling phenomena at the nanoscale.

Contribution

It introduces a novel method to spectroscopically map plexcitons at nanometer resolution, providing new insights into their coupling mechanisms and hybridization.

Findings

Nanoscale variation of Rabi splitting observed.

Plasmon-exciton detuning mapped at nanometer scale.

Evidence of strong coupling regime through absorption signals.

Abstract

Polaritons are compositional light-matter quasiparticles that have recently enabled remarkable breakthroughs in quantum and nonlinear optics, as well as in material science. Despite the enormous progress, however, a direct nanometer-scale visualization of polaritons has remained an open challenge. Here, we demonstrate that plasmon-exciton polaritons, or plexcitons, generated by a hybrid system composed of an individual silver nanoparticle and a few-layer transition metal dichalcogenide can be spectroscopically mapped with nanometer spatial resolution using electron energy loss spectroscopy in a scanning transmission electron microscope. Our experiments reveal important insights about the coupling process, which have not been reported so far. These include nanoscale variation of Rabi splitting and plasmon-exciton detuning, as well as absorption-dominated extinction signals, which in turn provide the ultimate evidence for the plasmon-exciton hybridization in the strong coupling regime. These findings pioneer new possibilities for in-depth studies of polariton-related phenomena with nanometer spatial resolution.