Double Exchange model for nanoscopic clusters

TL;DR

This paper provides an exact solution to the double exchange model on a nanoscopic six-site cluster, offering insights into magnetism at the nanoscale and evaluating the validity of approximation methods like DMFT.

Contribution

It introduces an exact solution for the double exchange model on a nanocluster, serving as a benchmark for studying magnetic correlations and testing approximation techniques.

Findings

Non-local correlations induce short-range magnetic order.

DMFT is reliable when non-local correlations are weak.

Exact solutions help validate approximation methods.

Abstract

We solve the double exchange model on nanoscopic clusters exactly, and specifically consider a six-site benzene-like nanocluster. This simple model is an ideal testbed for studying magnetism in nanoclusters and for validating approximations such as the dynamical mean field theory (DMFT). Non-local correlations arise between neighboring localized spins due to the Hund's rule coupling, favoring a short-range magnetic order of ferro- or antiferromagnetic type. For a geometry with more neighboring sites or a sufficiently strong hybridization between leads and the nanocluster, these non-local correlations are less relevant, and DMFT can be applied reliably.