Ferromagnetism in ABC-trilayer graphene

TL;DR

This paper investigates the ferromagnetic properties of ABC-stacked trilayer graphene using a tight-binding model with Coulomb interactions, revealing its enhanced robustness compared to other graphene forms.

Contribution

It provides the first detailed phase diagram of ferromagnetism in ABC-trilayer graphene considering both unscreened and screened Coulomb interactions.

Findings

Ferromagnetism is more robust in ABC-trilayer graphene than in monolayer, bilayer, and ABA-trilayer.

Screening reduces the ferromagnetic regime but the critical doping remains significantly higher.

The phase diagram shows the dependence of ferromagnetism on interaction strength and doping level.

Abstract

In this article we study the ferromagnetic behavior of ABC-stacked trilayer graphene. This is done using a nearest-neighbor tight-binding model, in the presence of long-range Coulomb interactions. For a given electron-electron interaction g and doping level n, we determine whether the total energy is minimized for a paramagnetic or ferromagnetic configuration of our variational parameters. The g versus n phase diagram is first calculated for the unscreened case. We then include the effects of screening using a simplified expression for the fermion bubble diagram. We show that ferromagnetism in ABC-trilayer graphene is more robust than in monolayer, in bilayer, and in ABA-trilayer graphene. Although the screening reduces the ferromagnetic regime in ABC-trilayer graphene, the critical doping level remains one order of magnitude larger than in unscreened bilayer graphene.