Magnetism of magic-angle twisted bilayer graphene

TL;DR

This study explores magnetic instabilities in charge-neutral twisted bilayer graphene near magic angles, revealing localized magnetic states at lower Coulomb interactions and highlighting the complex interplay of band flatness and localization.

Contribution

It introduces a combined real-space Hartree-Fock and dynamical mean-field approach to analyze magnetic states near magic angles, considering a rescaling method for large unit cells.

Findings

Localized magnetic states emerge at lower Coulomb interactions.

Rescaling overestimates magnetic effects, indicating complex band and localization interactions.

Insights suggest potential for experimental realization of magnetic states in twisted bilayer graphene.

Abstract

We investigate magnetic instabilities in charge-neutral twisted bilayer graphene close to so-called "magic angles" using a combination of real-space Hartree-Fock and dynamical mean-field theories. In view of the large size of the unit cell close to magic angles, we examine a previously proposed rescaling that permits to mimic the same underlying flat minibands at larger twist angles. We find that localized magnetic states emerge for values of the Coulomb interaction $U$ that are significantly smaller than what would be required to render an isolated layer antiferromagnetic. However, this effect is overestimated in the rescaled system, hinting at a complex interplay of flatness of the minibands close to the Fermi level and the spatial extent of the corresponding localized states. Our findings shed new light on perspectives for experimental realization of magnetic states in charge-neutral twisted bilayer graphene.