Magnetic Polarons in the 1D FM Kondo Model

TL;DR

This study uses Monte Carlo simulations to show that in one-dimensional ferromagnetic Kondo models, realistic parameters favor the formation of individual ferromagnetic polarons over phase separation, explaining spectral features and bandwidth behavior.

Contribution

It introduces an extended finite temperature uniform hopping approach (UHA) that incorporates polarons, providing a simple and effective way to understand the ferromagnetic Kondo model.

Findings

Double-exchange does not cause phase separation in 1D chains.

Ferromagnetic polarons explain the pseudogap in spectral functions.

Bandwidths are similar in ferromagnetic and paramagnetic phases due to polarons.

Abstract

The ferromagnetic Kondo model with classical corespins is studied via unbiased Monte-Carlo simulations. We show that with realistic parameters for the manganites and at low temperatures, the double-exchange mechanism does not lead to phase separation in one-dimensional chains but rather stabilizes individual ferromagnetic polarons. Within the ferromagnetic polaron picture, the pseudogap in the one-particle spectral function A_k(\omega) can easily be explained. Ferromagnetic polarons also clear up a seeming failure of the double-exchange mechanism in explaining the comparable bandwidths in the ferromagnetic and paramagnetic phase. For our analysis, we extend a simplified model, the finite temperature uniform hopping approach (UHA), to include polarons. It can easily be evaluated numerically and provides a simple quantitative understanding of the physical features of the ferromagnetic Kondo model.