Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene

Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene

11 Jan 2019 | Aaron L. Sharpe, Eli J. Fox, Arthur W. Barnard, Joe Finney, Kenji Watanabe, Takashi Taniguchi, M. A. Kastner, David Goldhaber-Gordon
This study reports the emergence of ferromagnetism in twisted bilayer graphene (TBG) near three-quarters (3/4) filling of the conduction miniband. The researchers observed a giant anomalous Hall (AH) effect with hysteresis and signs of chiral edge states in a narrow density range around an apparent insulating state at 3/4 filling. The magnetization of the sample can be reversed by applying a small DC current, suggesting the system is an incipient Chern insulator. The results indicate that the 3/4 filling state is a correlated Chern insulator, with a large AH effect and chiral edge conduction. The study also highlights the role of electron-electron interactions in driving the system into a ferromagnetic state, and the potential for TBG to serve as a platform for exploring quantum anomalous Hall (QAH) physics. The findings suggest that TBG could be a promising material for future applications in quantum computing and low-power electronics. The study was conducted using a "tear-and-stack" dry-transfer method and standard lithographic techniques to fabricate a TBG Hall bar device. The results demonstrate the potential of TBG as a new platform for QAH physics, with implications for metrology and quantum computing. The study also highlights the importance of understanding the magnetic order and topological character of correlated insulating states in TBG. The results suggest that TBG could be a promising material for future applications in quantum computing and low-power electronics.This study reports the emergence of ferromagnetism in twisted bilayer graphene (TBG) near three-quarters (3/4) filling of the conduction miniband. The researchers observed a giant anomalous Hall (AH) effect with hysteresis and signs of chiral edge states in a narrow density range around an apparent insulating state at 3/4 filling. The magnetization of the sample can be reversed by applying a small DC current, suggesting the system is an incipient Chern insulator. The results indicate that the 3/4 filling state is a correlated Chern insulator, with a large AH effect and chiral edge conduction. The study also highlights the role of electron-electron interactions in driving the system into a ferromagnetic state, and the potential for TBG to serve as a platform for exploring quantum anomalous Hall (QAH) physics. The findings suggest that TBG could be a promising material for future applications in quantum computing and low-power electronics. The study was conducted using a "tear-and-stack" dry-transfer method and standard lithographic techniques to fabricate a TBG Hall bar device. The results demonstrate the potential of TBG as a new platform for QAH physics, with implications for metrology and quantum computing. The study also highlights the importance of understanding the magnetic order and topological character of correlated insulating states in TBG. The results suggest that TBG could be a promising material for future applications in quantum computing and low-power electronics.
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