Importance of long-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene

TL;DR

This study shows that including long-range electron-electron interactions in models of twisted bilayer graphene significantly alters the predicted magnetic phases and enhances the range of twist angles where strong correlations occur, aligning well with experiments.

Contribution

The paper demonstrates the importance of long-range interactions in accurately modeling the magnetic phase diagram of twisted bilayer graphene, revealing qualitative differences from short-range models.

Findings

Long-range interactions lead to different magnetic order predictions.

Anti-ferromagnetic order is dominant at the magic angle.

Long-range interactions expand the twist angle range for strong correlations.

Abstract

Electron-electron interactions are intrinsically long ranged, but many models of strongly interacting electrons only take short-ranged interactions into account. Here, we present results of atomistic calculations including both long-ranged and short-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene and demonstrate that qualitatively different results are obtained when long-ranged interactions are neglected. In particular, we use Hartree theory augmented with Hubbard interactions and calculate the interacting spin susceptibility at a range of doping levels and twist angles near the magic angle to identify the dominant magnetic instabilities. At the magic angle, mostly anti-ferromagnetic order is found, while ferromagnetism dominates at other twist angles. Moreover, long-ranged interactions significantly increase the twist angle window in which strong correlation phenomena can be expected. These findings are in good agreement with available experimental data.