Ferromagnetic polarons in the one-dimensional ferromagnetic Kondo model with quantum mechanical S=3/2 core spins

TL;DR

This study uses numerical methods to analyze ferromagnetic polarons in a one-dimensional Kondo lattice model with quantum S=3/2 spins, revealing how Coulomb interactions and superexchange influence phase separation and polaron formation.

Contribution

It provides the first detailed quantum mechanical analysis of ferromagnetic polarons in the 1D Kondo model with S=3/2 spins, including Coulomb effects and phase diagrams.

Findings

Quantum fluctuations do not favor phase separation over polarons.

Coulomb repulsion induces phase separation at low superexchange J'.

Larger superexchange J' stabilizes ferromagnetic polarons.

Abstract

We present an extensive numerical study of the ferromagnetic Kondo lattice model with quantum mechanical S=3/2 core spins. We treat one orbital per site in one dimension using the density matrix renormalization group and include on-site Coulomb repulsion between the electrons. We examine parameters relevant to manganites, treating the range of low to intermediate doping, 0<x<0.5. In particular, we investigate whether quantum fluctuations favor phase separation over the ferromagnetic polarons observed in a model with classical core spins. We obtain very good agreement of the quantum model with previous results for the classical model, finding separated polarons which are repulsive at short distance for finite t_2g superexchange J'. Taking on-site Coulomb repulsion into account, we observe phase separation for small but finite superexchange J', while for larger J' polarons are favored in accordance with simple energy considerations previously applied to classical spins. We discuss the interpretation of compressibilities and present a phase diagram with respect to doping and the t_2g superexchange parameter J' with and without Coulomb repulsion.