Strong Momentum-Dependent Electron-Magnon Renormalization of a Surface Resonance on Iron

TL;DR

This study reveals a strong electron-magnon interaction on iron surfaces, leading to replica bands and significant band renormalization, highlighting the importance of magnetic excitations in electronic properties.

Contribution

It demonstrates the first observation of strong electron-magnon coupling causing replica-band formation on an iron surface, using spin- and angle-resolved photoemission.

Findings

Observation of replica bands at ~200 meV on iron surface

Strong magnetic linear dichroism indicating magnetic origin

Consistency with coupling to optical spin waves in Fe

Abstract

The coupling of fermionic quasiparticles to magnons is essential for a wide range of processes, from ultrafast magnetization dynamics in ferromagnets to Cooper pairing in superconductors. Although magnon energies are generally much larger than phonon energies, up to now their electronic band renormalization effect in ferromagnetic metals suggests a significantly weaker quasiparticle interaction. Here, using spin- and angle-resolved photoemission, we show an extraordinarily strong renormalization leading to replica-band formation of an iron surface resonance at ~200 meV. Its strong magnetic linear dichroism unveils the magnetic nature and momentum dependence of the energy renormalization. By determining the frequency- and momentum-dependent self-energy due to generic electron-boson interaction to compute the resultant electron spectral function, we show that the surface-state replica formation is consistent with strong coupling to an optical spin wave in a Fe thin film.