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

• Published in: Nature communications Vol. 15; no. 1; p. 3737
• Main Authors: Zhang, Hongyun, Li, Qian, Park, Youngju, Jia, Yujin, Chen, Wanying, Li, Jiaheng, Liu, Qinxin, Bao, Changhua, Leconte, Nicolas, Zhou, Shaohua, Wang, Yuan, Watanabe, Kenji, Taniguchi, Takashi, Avila, Jose, Dudin, Pavel, Yu, Pu, Weng, Hongming, Duan, Wenhui, Wu, Quansheng, Jung, Jeil, Zhou, Shuyun
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 03-05-2024; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/357/1018; 639/766/119/995; Asymmetry; Banded structure; Bilayers; Electric fields; Electronic structure; Electrons; Ferromagnetism; Graphene; Holes (electron deficiencies); Humanities and Social Sciences; Monolayers; multidisciplinary; Multilayers; Phase diagrams; Photoelectric emission; Science; Science (multidisciplinary); Spectroscopy
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-48166-8

Twisted bilayer graphene (tBLG) provides a fascinating platform for engineering flat bands and inducing correlated phenomena. By designing the stacking architecture of graphene layers, twisted multilayer graphene can exhibit different symmetries with rich tunability. For example, in twisted monolayer-bilayer graphene (tMBG) which breaks the
C
2
z
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 how the electronic structure evolves with electric field is critical for providing a better understanding of such asymmetric field-tunable properties. Here we report the experimental observation of field-tunable dichotomic electronic structure of tMBG by nanospot angle-resolved photoemission spectroscopy (NanoARPES) with operando gating. Interestingly, selective enhancement of the relative spectral weight contributions from monolayer and bilayer graphene is observed when switching the polarity of the bias voltage. Combining experimental results with theoretical calculations, the origin of such field-tunable electronic structure, resembling either tBLG or twisted double-bilayer graphene (tDBG), is attributed to the selectively enhanced contribution from different stacking graphene layers with a strong electron-hole asymmetry. Our work provides electronic structure insights for understanding the rich field-tunable physics of tMBG.
The phase diagram of twisted monolayer-bilayer graphene depends on the electric field direction, exhibiting phases similar to twisted bilayer and double-bilayer graphene. Here the authors study the field dependent electronic structure, in particular flat bands, using nano-ARPES and explain the field-tunability.