Ultrafast Momentum-Resolved Probing of Plasmon Thermal Dynamics with Free Electrons

TL;DR

This paper proposes a novel ultrafast electron microscopy technique that uses angle-resolved, energy-integrated inelastic electron scattering to study the momentum-resolved dynamics of plasmons in 2D materials like graphene, enabling detailed insights without complex spectrometers.

Contribution

It introduces a new method for probing ultrafast plasmon dynamics that bypasses the need for monochromatic electron beams and spectrometers, offering momentum resolution in time-resolved studies.

Findings

Predicts that angle-resolved inelastic scattering reveals plasmon dynamics

Shows the method can identify plasmon modes without spectrometers

Demonstrates potential for studying polaritons in 2D materials

Abstract

Current advances in ultrafast electron microscopy make it possible to combine optical pumping of a nanostructure and electron beam probing with sub{\aa}ngstrom and femtosecond spatiotemporal resolution. We present a theory predicting that this technique can reveal a rich out-of-equilibrium dynamics of plasmon excitations in graphene and graphite samples. In a disruptive departure from the traditional probing of nanoscale excitations based on the identification of spectral features in the transmitted electrons, we show that measurement of angle-resolved, energy-integrated inelastic electron scattering can trace the temporal evolution of plasmons in these structures and provide momentum-resolved mode identification, thus avoiding the need for highly-monochromatic electron beams and the use of electron spectrometers. This previously unexplored approach to study the ultrafast dynamics of optical excitations can be of interest to understand and manipulate polaritons in 2D semiconductors and other materials exhibiting a strong thermo-optical response.