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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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.
Extended data figures 1–7; references 30–35
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Superconductivity from valley fluctuations and approximate SO(4) symmetry in a weak coupling theory of twisted bilayer graphene
npj Quantum Materials (2019)
Nature Communications (2019)