Electron Recoil via Sample Momentum Transfer under Optical-Mode Excitation

TL;DR

This paper demonstrates experimentally how free electrons transfer momentum to planar samples during optical mode excitation, revealing effects on dispersion relations and momentum direction under specific conditions.

Contribution

First experimental observation of momentum transfer from free electrons to samples during optical excitation using momentum-resolved electron energy-loss spectroscopy.

Findings

Momentum transfer modifies the sample's dispersion relation.

Sample can receive momentum opposite to the electron beam.

Momentum transfer depends on sample tilt and excitation conditions.

Abstract

The interaction between free electrons and optical modes underlies a variety of quantum and nanoscale light-matter phenomena, yet the associated momentum exchange with the sample largely remained overlooked. Here, we experimentally demonstrate the momentum transfer from free electrons to planar samples during optical mode excitation using momentum-resolved electron energy-loss spectroscopy. The momentum transfer to the sample modifies the apparent dispersion relation which is significant when the planner sample is tilted. Under specific conditions, the sample receives momentum opposite to the electron beam direction.