Layer-polarized ferromagnetism in rhombohedral multilayer graphene

Wenqiang Zhou; Jing Ding; Jiannan Hua; Le Zhang; Kenji Watanabe; Takashi Taniguchi; Wei Zhu; Shuigang Xu

doi:10.1038/s41467-024-46913-5

論文 Layer-polarized ferromagnetism in rhombohedral multilayer graphene

Wenqiang Zhou ; Jing Ding ; Jiannan Hua ; Le Zhang ; Kenji Watanabe (National Institute for Materials Science) ; Takashi Taniguchi (National Institute for Materials Science) ; Wei Zhu ; Shuigang Xu

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Wenqiang Zhou, Jing Ding, Jiannan Hua, Le Zhang, Kenji Watanabe, Takashi Taniguchi, Wei Zhu, Shuigang Xu. Layer-polarized ferromagnetism in rhombohedral multilayer graphene. Nature Communications. 2024, 15 (1), 2597. https://doi.org/10.1038/s41467-024-46913-5

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(abstract)

The topological electronic structure of crystalline materials often gives rise to intriguing surface states, such as Dirac surface states in topological insulators, Fermi arc surface states in Dirac semimetals, and topological superconductivity in iron-based superconductors. Recently, rhombohedral multilayer graphene has emerged as a promising platform for exploring exotic surface states due to its hosting of topologically protected surface flat bands at low energy, with the layer-dependent energy dispersion. These flat bands can promote electron correlations, leading to a plethora of quantum phenomena, including spontaneous symmetry breaking, superconductivity, ferromagnetism, and topological Chern insulators. Nevertheless, the intricate connection between the surface flat bands in rhombohedral multilayer graphene and the highly dispersive high-energy bands hinders the exploration of correlated surface states. Here, we present a method to isolate the surface flat bands of rhombohedral heptalayer (7L) graphene by introducing moiré superlattices. The pronounced screening effects observed in the moiré potential-modulated rhombohedral 7L graphene indicate its essential three-dimensional (3D) nature. The isolated surface flat bands favor correlated states on the surface in the regions away from charge-neutrality points. Most notably, we observe tunable surface ferromagnetism, manifested as an anomalous Hall effect with hysteresis loops, which is achieved by polarizing surface states using finite displacement fields. Our work establishes rhombohedral multilayer graphene moiré superlattice as a unique 3D system for exploring correlated surface states.

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