# Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene

## TL;DR

This study demonstrates that twisted bilayer graphene near three-quarters filling exhibits emergent ferromagnetism, anomalous Hall effects, and signs of chiral edge states, driven by strong electron interactions in flat minibands.

## Contribution

It provides experimental evidence of ferromagnetism and chiral edge states in twisted bilayer graphene at 3/4 filling, indicating a possible incipient Chern insulator state.

## Key findings

- Emergent ferromagnetic hysteresis observed.
- Giant anomalous Hall effect up to 10.4 kΩ.
- Signs of chiral edge states near insulating state.

## Abstract

When two sheets of graphene are stacked at a small twist angle, the resulting flat superlattice minibands are expected to strongly enhance electron-electron interactions. Here we present evidence that near three-quarters ($3/4$) filling of the conduction miniband these enhanced interactions drive the twisted bilayer graphene into a ferromagnetic state. We observe emergent ferromagnetic hysteresis, with a giant anomalous Hall (AH) effect as large as $10.4\ \mathrm{k\Omega}$ and signs of chiral edge states in a narrow density range around an apparent insulating state at $3/4$. Surprisingly, the magnetization of the sample can be reversed by applying a small DC current. Although the AH resistance is not quantized and dissipation is significant, we suggest that the system is an incipient Chern insulator.