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arXiv · 1908.11718

Giant Orbital Magneto-electric effect and Current-driven Magnetization Switching in Twisted Bilayer Graphene

Wen-Yu He·David Goldhaber-Gordon·K. T. Law
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Abstract

Recently, signatures of quantum anomalous Hall states with spontaneous ferromagnetism were observed in twisted bilayer graphenes (TBGs) near 3/4 filling [1, 2]. Importantly, it was demon-strated that an extremely small current can switch the direction of the magnetization. This offers the prospect of realizing low energy dissipation magnetic memories. However, the mechanism of the current-driven magnetization switching is poorly understood as the charge currents in graphene layers are generally believed to be non-magnetic. In this work, we demonstrate that, in TBGs, the twist-induced reduction of lattice symmetry allows a charge current to generate net orbital magnetization at a general filling factor through magnetoelectric effects. Substrate-induced strain and sublattice symmetry breaking further reduce the symmetry such that an out-of-plane orbital magnetization can be generated. Due to the large non-trivial Berry phase of the flat bands, the orbital magnetization of a Bloch state can be as large as tens of Bohr magnetons and therefore a small current would be sufficient to generate a large orbital magnetization. We further demonstrate how the charge current with orbital magnetization can switch the magnetization of the quantum anomalous Hall state near 3/4 filling as observed in the experiments [1, 2].

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Wen-Yu He, David Goldhaber-Gordon, K. T. Law. 2019-08-30. Giant Orbital Magneto-electric effect and Current-driven Magnetization Switching in Twisted Bilayer Graphene. https://doi.org/10.1038/s41467-020-15473-9

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