Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene

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 ([Formula: see text]) filling of the conduction miniband, these enhanced inter...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2019-08, Vol.365 (6453), p.605-608
Main Authors: Sharpe, Aaron L, Fox, Eli J, Barnard, Arthur W, Finney, Joe, Watanabe, Kenji, Taniguchi, Takashi, Kastner, M A, Goldhaber-Gordon, David
Format: Article
Language:English
Subjects:
Bilayers
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
Conduction
Density
Direct current
Ferromagnetism
Gating
Graphene
Hall effect
MATERIALS SCIENCE
Superconductivity
Superlattices
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Summary: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 ([Formula: see text]) filling of the conduction miniband, these enhanced interactions drive the twisted bilayer graphene into a ferromagnetic state. In a narrow density range around an apparent insulating state at [Formula: see text], we observe emergent ferromagnetic hysteresis, with a giant anomalous Hall (AH) effect as large as 10.4 kilohms and indications of chiral edge states. Notably, the magnetization of the sample can be reversed by applying a small direct current. Although the AH resistance is not quantized, and dissipation is present, our measurements suggest that the system may be an incipient Chern insulator.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.aaw3780