Magnon self energy in the correlated ferromagnetic Kondo lattice model: spin-charge coupling effects on magnon excitations in manganites

TL;DR

This paper calculates magnon self energy in the correlated ferromagnetic Kondo lattice model, revealing that correlation effects minimally influence magnon energies and that doping-dependent magnon softening likely results from spin-orbital coupling.

Contribution

It introduces a diagrammatic expansion scheme that preserves spin symmetry and systematically incorporates correlation effects in the FKLM.

Findings

Magnon energies are nearly unaffected by correlation effects at intermediate coupling.

Magnon dispersion retains Heisenberg form at high band fillings.

Doping-dependent magnon softening is attributed to spin-orbital coupling, not correlations.

Abstract

Magnon self energy due to spin-charge coupling is calculated for the correlated ferromagnetic Kondo lattice model using a diagrammatic expansion scheme. Systematically incorporating correlation effects in the form of self-energy and vertex corrections, the expansion scheme explicitly preserves the continuous spin rotation symmetry and hence the Goldstone mode. Due to a near cancellation of the correlation-induced quantum correction terms at intermediate coupling and optimal band filling relevant for ferromagnetic manganites, the renormalized magnon energies for the correlated FKLM are nearly independent of correlation term. Even at higher band fillings, despite exhibiting overall non-Heisenberg behavior, magnon dispersion in the \Gamma-X direction retains nearly Heisenberg form. Therefore, the experimentally observed doping dependent zone-boundary magnon softening must be ascribed to spin-orbital coupling effects.