Fermionic representation for the ferromagnetic Kondo lattice model -- diagrammatic study of spin-charge coupling effects on magnon excitations

TL;DR

This paper introduces a fermionic approach to study the ferromagnetic Kondo lattice model, enabling the analysis of correlation effects on magnon excitations and explaining experimental anomalies in manganites.

Contribution

It develops a fermionic representation and a systematic inverse-degeneracy expansion to analyze spin-charge coupling effects on magnons while preserving spin-rotation symmetry.

Findings

Magnon damping is significantly enhanced at strong interactions.

Zone boundary magnon softening explains experimental anomalies.

Correlation effects are incorporated via self-energy and vertex corrections.

Abstract

A purely fermionic representation is introduced for the ferromagnetic Kondo lattice model which allows conventional diagrammatic tools to be employed to study correlation effects. Quantum 1/S corrections to magnon excitations are investigated using a systematic inverse-degeneracy expansion scheme which incorporates correlation effects in the form of self-energy and vertex corrections, while explicitly preserving the continuous spin-rotation symmetry. Magnon self-energy is studied in the full range of interaction strength, and shown to result in strong magnon damping and anomalous softening for zone boundary modes, which accounts for several zone-boundary anomalies observed in recent spin-wave measurements of ferromagnetic manganites.