Antiferromagnetism in the Hubbard Model on the Bernal-stacked Honeycomb Bilayer

TL;DR

This study investigates antiferromagnetism in a bilayer graphene model using advanced computational methods, revealing a robust magnetic order driven by Coulomb interactions and characterized by inhomogeneous spin moments.

Contribution

It combines quantum Monte Carlo, functional renormalization group, and mean-field theory to analyze magnetic ordering in the Hubbard model on Bernal-stacked honeycomb bilayers, highlighting inhomogeneous spin participation.

Findings

Antiferromagnetic order emerges due to finite density of states at Fermi level.

Enhanced moments are observed at three-fold coordinated sites.

The magnetic state remains stable with increased interlayer and Coulomb interactions.

Abstract

Using a combination of quantum Monte Carlo simulations, functional renormalization group calculations and mean-field theory, we study the Hubbard model on the Bernal-stacked honeycomb bilayer at half-filling as a model system for bilayer graphene. The free bands consisting of two Fermi points with quadratic dispersions lead to a finite density of states at the Fermi level, which triggers an antiferromagnetic instability that spontaneously breaks sublattice and spin rotational symmetry once local Coulomb repulsions are introduced. Our results reveal an inhomogeneous participation of the spin moments in the ordered ground state, with enhanced moments at the three-fold coordinated sites. Furthermore, we find the antiferromagnetic ground state to be robust with respect to enhanced interlayer couplings and extended Coulomb interactions.