Evidence of Gate-Tunable Mott Insulator in Trilayer Graphene-Boron Nitride Moir\'e Superlattice

TL;DR

This paper reports the experimental realization of a gate-tunable Mott insulator in ABC trilayer graphene on hBN, demonstrating control over correlated insulating states via electrical gating in a moiré superlattice system.

Contribution

It introduces a tunable Mott insulator in a graphene-based heterostructure with in situ control over the Mott gap and electron filling, advancing the study of strongly correlated physics.

Findings

Mott insulator states at 1/4 and 1/2 fillings in TLG/hBN heterostructure.

Mott gap can be modulated by vertical electric field.

Electron doping can switch between different Mott insulating states.

Abstract

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. 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-temperature superconductivity. 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 (TLG) and hexagonal boron nitride (hBN) heterostructure with a moir\'e superlattice. Unlike massless Dirac electrons in monolayer graphene, electrons in pristine ABC TLG are characterized by quartic energy dispersion and large effective mass that are conducive for strongly correlated phenomena. The moir\'e superlattice in TLG/hBN heterostructures leads to narrow electronic minibands that are gate tunable. Each filled miniband contains 4 electrons in one moir\'e lattice site due to the spin and valley degeneracy of graphene. The Mott insulator states emerge at 1/4 and 1/2 fillings, corresponding to one electron and two electrons per site, respectively. Moreover, the Mott states in the ABC TLG/hBN heterostructure exhibit unprecedented tunability: the Mott gap can be modulated in situ by a vertical electrical field, and at the meantime, 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\'e superlattice heterostructures.