Imaging topological and correlated insulating states in twisted monolayer-bilayer graphene

Si-Yu Li; Zhengwen Wang; Yucheng Xue; Yingbo Wang; Shihao Zhang; Jianpeng Liu; Zheng Zhu; Kenji Watanabe; Takashi Taniguchi; Hong-Jun Gao; Yuhang Jiang; Jinhai Mao

doi:10.1038/s41467-022-31851-x

Imaging topological and correlated insulating states in twisted monolayer-bilayer graphene

Nat Commun. 2022 Jul 22;13(1):4225. doi: 10.1038/s41467-022-31851-x.

Authors

Si-Yu Li^#^{1

2

3}, Zhengwen Wang^#^{1

2}, Yucheng Xue¹, Yingbo Wang¹, Shihao Zhang⁴, Jianpeng Liu⁴, Zheng Zhu⁵, Kenji Watanabe⁶, Takashi Taniguchi⁶, Hong-Jun Gao^{1

3}, Yuhang Jiang⁷, Jinhai Mao⁸

Affiliations

¹ School of Physical Sciences and CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100049, China.
² College of Materials Science and Optoelectronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, 100049, China.
³ Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
⁴ School of Physical Science and Technology, ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai, 201210, China.
⁵ Kavli Institute for Theoretical Sciences and CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100190, China.
⁶ Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, 305-0044, Japan.
⁷ College of Materials Science and Optoelectronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, 100049, China. yuhangjiang@ucas.ac.cn.
⁸ School of Physical Sciences and CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100049, China. jhmao@ucas.ac.cn.

^# Contributed equally.

Abstract

Flat bands in Van der Waals heterostructure provide an ideal platform for unveiling emergent quantum electronic phases. One celebrated example is twisted monolayer-bilayer graphene, in which the effects of electronic correlation have been observed. Here, we report the observation via scanning tunnelling microscopy and spectroscopy of correlated insulating states in twisted monolayer-bilayer graphene, leading to the formation of an electron crystal phase. At integer fillings, the strong Coulomb interaction redistributes flat-band electrons within one moiré unit cell, producing an insulating state with vanishing density of states at the Fermi level. Moreover, our approach enables the direct visualization of an ordered lattice of topological torus-shaped states, generated by the interaction between the electron crystal and the non-trivial band topology of twisted monolayer-bilayer graphene. Our results illustrate an efficient strategy for entwining topological physics with strong electron correlation in twisted van der Waals structures.

Abstract

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