Electric field-tunable layer polarization in graphene/boron nitride twisted quadrilayer superlattices

TL;DR

This paper develops a continuum model to study how electric fields and twist angles influence layer polarization and band structure in graphene/hBN and graphene/graphene heterostructures, revealing tunable ferroelectric-like behavior.

Contribution

It introduces a low-energy continuum model for twisted multilayer graphene heterostructures, highlighting electric field and twist angle effects on layer polarization and band flattening.

Findings

Twist angle asymmetry induces layer polarization in graphene/hBN heterostructures.

Out-of-plane displacement fields tune layer polarization and flatten bands.

External electric fields can similarly tune electronic structures in quadrilayer graphene.

Abstract

The recently observed unconventional ferroelectricity in AB bilayer graphene sandwiched by hexagonal Boron Nitride (hBN) presents a new platform to manipulate correlated phases in multilayered van der Waals heterostructures. We present a low-energy continuum model for AB bilayer graphene encapsulated by the top and bottom layers of either hBN or graphene, with two independent twist angles. For the graphene/hBN heterostructures, we show that twist angle asymmetry leads to a layer polarization of the valence and conduction bands. We also show that an out-of-plane displacement field not only tunes the layer polarization but also flattens the low-energy bands. We extend the model to show that the electronic structures of quadrilayer graphene heterostructure consisting of AB bilayer graphene encapsulated by the top and bottom graphene layers can similarly be tuned by an external electric field.