Unconventional Orbital Magnetism in Graphene-based Fractional Chern Insulators

Jian Xie; Zaizhe Zhang; Xi Chen; Yves H. Kwan; Zihao Huo; Jonah Herzog-Arbeitman; Liangliang Guo; Kenji Watanabe; Takashi Taniguchi; Kaihui Liu; X. C. Xie; B. Andrei Bernevig; Zhi-Da Song; Xiaobo Lu

arXiv · 2506.01485

Unconventional Orbital Magnetism in Graphene-based Fractional Chern Insulators

Jian Xie·Zaizhe Zhang·Xi Chen·Yves H. Kwan·Zihao Huo·Jonah Herzog-Arbeitman·Liangliang Guo·Kenji Watanabe·Takashi Taniguchi·Kaihui Liu·X. C. Xie·B. Andrei Bernevig·Zhi-Da Song·Xiaobo Lu

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Abstract

Orbital magnetism in graphene originates from correlation-driven spontaneous valley symmetry breaking1-7. It can lead to various anomalous transport phenomena such as integer and fractional quantum anomalous Hall effects8-11. In general, the in-plane magnetic field B|| primarily couples to the spin degrees of freedom in graphene and has long been presumed to have a negligible effect on orbital magnetism due to the ultra-weak spin-orbit coupling12-18. In this work, we report multiple unconventional orbital magnetic phenomena that are highly sensitive to the B|| field in graphene/hBN superlattices hosting both integer and fractional Chern insulators (FCIs). We observed chirality-switching behaviors of the Chern insulator at moir\'e filling factor {\nu} = 1 under a finite B_par, demonstrating that both the C = +-1 states are permissible ground states at zero perpendicular magnetic field B_per. For the FCI at {\nu} = 2/3, we observed topological phase transitions between two states characterized by Hall resistivity \r{ho}xy = +-3h/2e2 under both B_per and B_par fields. In-plane B|| field can effectively suppress the FCI state at zero B_per field and enhance the FCI state with the opposite chirality, as resolved in Landau fan diagrams. Moreover, we observed rich phase transitions at 1 < {\nu} < 2, accompanied by intervalley coherence and anomalous Hall effects (AHE) that can be triggered by sweeping either B_per or B_par. Our work has unveiled new properties of orbital magnetism, providing a new knob for engineering various AHE in graphene.

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Jian Xie, Zaizhe Zhang, Xi Chen, Yves H. Kwan, Zihao Huo, Jonah Herzog-Arbeitman, Liangliang Guo, Kenji Watanabe, Takashi Taniguchi, Kaihui Liu, X. C. Xie, B. Andrei Bernevig, Zhi-Da Song, Xiaobo Lu. 2025-06-02. Unconventional Orbital Magnetism in Graphene-based Fractional Chern Insulators. https://arxiv.org/abs/2506.01485

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