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Evidence of Gate-Tunable Mott Insulator in Trilayer Graphene-Boron Nitride Moire Superlattice

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University of California at Berkeley Berkeley United States

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Mott insulator plays a central role in strongly correlated physics, where the repulsive Coulomb interaction dominates over the electron kinetic energy and leads to insulating states with one electron occupying each unit cell.1,2 Doped Mott insulator is often described by the Hubbard model3, which can give rise to other correlated phenomena such as unusual magnetism and even high temperaturesuperconductivity2,4. 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 realization of such a tunable Mott insulator in the ABC trilayer graphene TLGand hexagonal boron nitride hBN heterostructure with a moir superlattice. Unlike massless Dirac electrons in monolayer graphene5,6, electrons in pristine ABCTLG are characterized by quartic energy dispersion and large effective mass7-11 that are conducive for strongly correlated phenomena. The moir superlattice12-18 inTLGhBN heterostructures leads to narrow electronic minibands that are gate-tunable. Each filled miniband contains 4 electrons in one moir lattice site due to the spin and valley degeneracy of graphene. The Mott insulator states emerge at 14 and12 fillings, corresponding to one electron and two electrons per site, respectively. Moreover, the Mott states in the ABC TLGhBN heterostructure exhibit unprecedented tunability the Mott gap can be modulated in situ by a vertical electrical field, and at the mean time the electron doping can be gate-tuned to fill the band from one Mott insulating state to another. Our observation of a tunable Mott insulator opens up exciting opportunities to explore novel strongly correlated phenomena in two-dimensional moir superlattice heterostructures.

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  • Solid State Physics
  • Crystallography

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