Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride

TL;DR

This study reveals charge-polarized superlattices in twisted hexagonal boron nitride, showing ferroelectric-like domains caused by interfacial elastic deformations, which could enable new van der Waals heterostructure designs.

Contribution

First observation of ferroelectric-like domains in twisted hBN, linking interfacial elastic deformations to charge polarization and superlattice formation.

Findings

Ferroelectric-like domains form in twisted hBN with large surface potential.

Domains are independent of size, orientation, and thickness of hBN.

Modeling confirms out-of-plane polarized dipoles due to interfacial deformations.

Abstract

When two-dimensional crystals are brought into close proximity, their interaction results in strong reconstruction of electronic spectrum and local crystal structure. Such reconstruction strongly depends on the twist angle between the two crystals and has received growing attention due to new interesting electronic and optical properties that arise in graphene and transitional metal dichalcogenides. Similarly, novel and potentially useful properties are expected to appear in insulating crystals. Here we study two insulating crystals of hexagonal boron nitride (hBN) stacked at a small twist angle. Using electrostatic force microscopy, we observe ferroelectric-like domains arranged in triangular superlattices with a large surface potential that is independent on the size and orientation of the domains as well as the thickness of the twisted hBN crystals. The observation is attributed to interfacial elastic deformations that result in domains with a large density of out-of-plane polarized dipoles formed by pairs of boron and nitrogen atoms belonging to the opposite interfacial surfaces. This effectively creates a bilayer-thick ferroelectric with oppositely polarized (BN and NB) dipoles in neighbouring domains, in agreement with our modelling. The demonstrated electrostatic domains and their superlattices offer many new possibilities in designing novel van der Waals heterostructures.