Realization of Topological Mott Insulator in a Twisted Bilayer Graphene Lattice Model

TL;DR

This paper demonstrates the realization of a topological Mott insulator in twisted bilayer graphene by using large-scale simulations to reveal a phase transition to a quantum anomalous Hall state driven by strong electron interactions.

Contribution

It provides the first large-scale lattice model study showing the emergence of a topological Mott insulator in twisted bilayer graphene, highlighting the strong coupling mechanism.

Findings

Identification of a first-order phase transition between stripe insulator and quantum anomalous Hall states.

Confirmation of the quantum anomalous Hall state at three-quarters filling.

Evidence of a topological Mott insulator driven by Coulomb interactions.

Abstract

Magic-angle twisted bilayer graphene has recently become a thriving material platform realizing correlated electron phenomena taking place within its topological flat bands. Several numerical and analytical methods have been applied to understand the correlated phases therein, revealing some similarity with the quantum Hall physics. In this work, we provide a Mott-Hubbard perspective for the TBG system. Employing the large-scale density matrix renormalization group on the lattice model containing the projected Coulomb interactions only, we identify a first-order quantum phase transition between the insulating stripe phase and the quantum anomalous Hall state with the Chern number of $\pm 1$. Our results not only shed light on the mechanism of the quantum anomalous Hall state discovered at three-quarters filling, but also provide an example of the topological Mott insulator, i.e., the quantum anomalous Hall state in the strong coupling limit.