Electron-electron interactions and the phase diagram of a graphene bilayer

TL;DR

This paper investigates how electron-electron interactions influence the phase diagram of graphene bilayers, revealing instabilities and magnetic orderings driven by Coulomb and short-range interactions.

Contribution

It introduces a variational wavefunction approach to analyze the effects of long and short-range interactions on bilayer graphene's phases.

Findings

Long-range Coulomb interactions cause instability to electron and hole pockets with ferromagnetic polarization.

Short-range interactions induce c-axis antiferromagnetic order between layers.

Doping and band distortions also affect the magnetic and electronic phases.

Abstract

We study the effects of long and short-range electron-electron interactions in a graphene bilayer. Using a variational wavefunction technique we show that in the presence of long-range Coulomb interactions the clean bilayer is always unstable to electron and hole pocket formation with a finite ferromagnetic polarization. Furthermore, we argue that short-range electron-electron interactions lead to a staggered orientation of the ordered ferromagnetic moment in each layer (that is, c-axis antiferromagnetism). We also comment on the effects of doping and trigonal distortions of the electronic bands.