Theory of Momentum-Resolved Electron Energy-Loss Spectra of Coupled Phonon and Magnon Excitations

TL;DR

This paper presents a comprehensive theory for momentum-resolved electron energy-loss spectra in STEM-EELS, incorporating coupled phonon and magnon excitations, and demonstrates its application to iron at room temperature.

Contribution

It introduces an advanced formalism combining phonon-magnon interactions with atomistic spin-lattice dynamics for accurate EELS simulation.

Findings

Identification of non-additive spectral features due to phonon-magnon coupling

Simulation of EELS signals including multiple scattering effects

Estimation of electron dose for magnon detection

Abstract

We develop a theory of momentum-resolved electron energy-loss spectra in the scanning transmission microscope (STEM-EELS) that captures the effects of coupled phonon and magnon excitations within a unified formalism, and apply it to body-centered cubic iron at 300 K. By advancing the Time Autocorrelation of Auxiliary Wavefunctions (TACAW) method to incorporate atomistic spin-lattice dynamics (ASLD), we simulate the EELS signal, including phonon-magnon interaction effects, dynamical diffraction, and multiple scattering. Our results reveal non-additive spectral features arising from phonon-magnon coupling, hybridization, and energy shifts, and further allow estimation of the electron dose required to detect magnon scattering under optimized detector conditions.