Ferromagnetism without flat bands in thin armchair nanoribbons

TL;DR

This paper demonstrates that thin armchair graphene nanoribbons can exhibit ferromagnetism at low electron concentrations without the presence of flat bands, due to correlations and confinement effects.

Contribution

It reveals a new mechanism for ferromagnetism in nanoribbons independent of flat band conditions, using an exact Hubbard model analysis.

Findings

Ferromagnetic ground state at low concentrations in non-flat band systems

Metallic behavior coexists with ferromagnetism in the studied nanoribbons

Correlation and confinement effects drive ferromagnetism without flat bands

Abstract

Describing by a Hubbard type of model a thin armchair graphene ribbon in the armchair hexagon chain limit, one shows in exact terms, that even if the system does not have flat bands at all, at low concentration a mesoscopic sample can have ferromagnetic ground state, being metallic in the same time. The mechanism is connected to a common effect of correlations and confinement.