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Evidence of a gate-tunable Mott insulator in a trilayer graphene moiré superlattice

Nature Physics volume 15, pages 237–241 (2019)Cite this article

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Abstract

The Mott insulator is a central concept in strongly correlated physics and manifests when the repulsive Coulomb interaction between electrons dominates over their kinetic energy1,2. Doping additional carriers into a Mott insulator can give rise to other correlated phenomena such as unusual magnetism and even high-temperature superconductivity2,3. A tunable Mott insulator, where the competition between the Coulomb interaction and the kinetic energy can be varied in situ, can provide an invaluable model system for the study of Mott physics. Here we report the possible realization of such a tunable Mott insulator in a trilayer graphene heterostructure with a moiré superlattice. The combination of the cubic energy dispersion in ABC-stacked trilayer graphene4,5,6,7,8 and the narrow electronic minibands induced by the moiré potential9,10,11,12,13,14,15 leads to the observation of insulating states at the predicted band fillings for the Mott insulator. Moreover, the insulating states in the heterostructure can be tuned: the bandgap can be modulated by a vertical electrical field, and at the same time the electron doping can be modified by a gate to fill the band from one insulating state to another. This opens up exciting opportunities to explore strongly correlated phenomena in two-dimensional moiré superlattice heterostructures.

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Fig. 1: ABC-TLG/hBN moiré superlattice and dual gate FET.
Fig. 2: Transport of gate-tunable Mott state.
Fig. 3: Temperature-dependent resistivity.
Fig. 4: Single-particle band structure of ABC-TLG/hBN moiré superlattice.

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Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

The authors thank C. Jin, E. Regan, X. Lu, Y. Shan, S. Wu and G. Zhang for discussions and help with sample preparation. The trilayer graphene sample fabrication and experimental study was supported by the Office of Naval Research (award no. N00014-15-1-2651). The initial idea and proof-of-principle calculation of 2D flatband engineering was supported by an ARO MURI award (W911NF-15-1-0447). Part of the sample fabrication was conducted at the Nano-fabrication Laboratory at Fudan University. B.L.C. was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2018R1A6A1A06024977) and by grants NRF-2016R1A2B4010105 and NRF-2017R1D1A1B03035932. J.J. was supported by the Samsung Science and Technology Foundation under project no. SSTF-BA1802-06. Y.Z. acknowledges financial support from the National Key Research Program of China (grant nos. 2016YFA0300703 and 2018YFA0305600), the NSF of China (grant nos. U1732274, 11527805, 11425415 and 11421404), Shanghai Municipal Science and Technology Commission (grant no. 18JC1410300) and the Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDB30000000). Z.S. is supported by the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning and the National Natural Science Foundation of China under grant no. 11574204. B.L., H.L. and Z.S. are supported by the National Key Research and Development Program of China (grant 2016YFA0302001) and National Natural Science Foundation of China (grants 11574204, 11774224). Growth of hBN crystals was supported by the Elemental Strategy Initiative conducted by the MEXT, Japan and JSPS KAKENHI grant no. JP15K21722. Part of the sample fabrication was conducted at Fudan Nano-fabrication Lab.

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Authors and Affiliations

  1. Department of Physics, University of California at Berkeley, Berkeley, CA, USA

    Guorui Chen, Lili Jiang & Feng Wang

  2. State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China

    Guorui Chen & Yuanbo Zhang

  3. Collaborative Innovation Center of Advanced Microstructures, Nanjing, China

    Guorui Chen, Bosai Lyu, Hongyuan Li, Zhiwen Shi & Yuanbo Zhang

  4. Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA, USA

    Shuang Wu

  5. Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China

    Bosai Lyu, Hongyuan Li & Zhiwen Shi

  6. Department of Physics, University of Seoul, Seoul, Korea

    Bheema Lingam Chittari & Jeil Jung

  7. National Institute for Materials Science, Tsukuba, Japan

    Kenji Watanabe & Takashi Taniguchi

  8. Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai, China

    Yuanbo Zhang

  9. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Feng Wang

  10. Kavli Energy NanoSciences Institute at the University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Feng Wang

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  1. Guorui Chen
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Contributions

F.W. and Y.Z. supervised the project. G.C. fabricated samples and performed transport measurements. G.C., L.J., S.W., B.L., H.L. and Z.S. prepared trilayer graphene and performed near-field infrared and atomic force microscopy measurements. B.L.C. and J.J. calculated the band structures. K.W. and T.T. grew hBN single crystals. G.C., Y.Z. and F.W. analysed the data.

Corresponding authors

Correspondence to Yuanbo Zhang or Feng Wang.

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Extended Data

Extended data figures 1–7; references 30–35

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Chen, G., Jiang, L., Wu, S. et al. Evidence of a gate-tunable Mott insulator in a trilayer graphene moiré superlattice. Nat. Phys. 15, 237–241 (2019). https://doi.org/10.1038/s41567-018-0387-2

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