Observation of dichotomic field-tunable electronic structure in twisted monolayer-bilayer graphene

Hongyun Zhang; Qian Li; Youngju Park; Yujin Jia; Wanying Chen; Jiaheng Li; Qinxin Liu; Changhua Bao; Nicolas Leconte; Shaohua Zhou; Yuan Wang; Kenji Watanabe; Takashi Taniguchi; Jose Avila; Pavel Dudin; Pu Yu; Hongming Weng; Wenhui Duan; Quansheng Wu; Jeil Jung; Shuyun Zhou

doi:10.1038/s41467-024-48166-8

Journal article Observation of dichotomic field-tunable electronic structure in twisted monolayer-bilayer graphene

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Hongyun Zhang, Qian Li, Youngju Park, Yujin Jia, Wanying Chen, Jiaheng Li, Qinxin Liu, Changhua Bao, Nicolas Leconte, Shaohua Zhou, Yuan Wang, Kenji Watanabe, Takashi Taniguchi, Jose Avila, Pavel Dudin, Pu Yu, Hongming Weng, Wenhui Duan, Quansheng Wu, Jeil Jung, Shuyun Zhou. Observation of dichotomic field-tunable electronic structure in twisted monolayer-bilayer graphene. Nature Communications. 2024, 15 (1), 3737. https://doi.org/10.1038/s41467-024-48166-8

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Twisted bilayer graphene (tBLG) provides a fascinating platform for engineering flat bands and inducing correlated phenomena. By increasing the number of stacked graphene layers, twisted multilayer graphene can exhibit different symmetries with rich tunabilities. For example, for twisted monolayer-bilayer graphene (tMBG) which breaks the C2z symmetry, transport measurements reveal an asymmetric phase diagram under an out-of-plane electric field, exhibiting correlated insulating state and ferromagnetic state respectively when reversing the field direction. Revealing the electronic structure evolution with electric field is critical for understanding such asymmetric field tunable properties. Here we report the experimental observation of dichotomic electronic structure response of tMBG to bias voltage by nanospot angle-resolved photoemission spectroscopy (NanoARPES) with operando gating. Spectral weight contributions from monolayer and bilayer graphene are selectively enhanced by switching the bias voltage, and dispersive bands similar to tBLG are observed under positive bias voltage (electric field pointing from monolayer to bilayer graphene), while in contrast, more pronounced flat bands resembling those in twisted double bilayer graphene (tDBG) are observed under negative bias voltage. Combing experimental results with theo- retical calculations, the origin of such field tunable electronic structure is attributed to the field induced population of carriers into different stacked graphene layers with enhanced electron-hole asymmetry dictated by the asymmetric stacking. Our work provides electronic structure insights for understanding the rich field-tunable physics of tMBG.

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