Ferroelectricity in twisted double bilayer graphene

TL;DR

This paper demonstrates ferroelectric hysteresis in twisted double bilayer graphene, revealing intrinsic switchable polarization in moiré superlattices without the need for additional layers, advancing 2D ferroelectric research.

Contribution

It reports the first observation of ferroelectricity in twisted double bilayer graphene, showing intrinsic polarization without external layers, and highlights the potential of moiré superlattices for 2D ferroelectricity.

Findings

Ferroelectric hysteresis observed in TDBG system.

Switchable polarization in AB-BA stacking without BN layers.

Polarized domains depend on stacking and external fields.

Abstract

Two-dimensional ferroelectrics can maintain vertical polarization up to room temperature, and are, therefore, promising for next-generation nonvolatile memories. Although natural two-dimensional ferroelectrics are few, moir\'{e} superlattices provide us with a generalized method to construct ferroelectrics from non-ferroelectric parent materials. We report a realization of ferroelectric hysteresis in a AB-BA stacked twisted double bilayer graphene (TDBG) system. The ferroelectric polarization is prominent at zero external displacement field and reduces upon increasing displacement fields. TDBG in the AB-BA configuration possesses a superlattice of non-centrosymmetric domains, exhibiting alternatively switchable polarities even without the assistance of any boron nitride layers; however, in the AB-AB stacking case, the development of polarized domains necessitates the presence of a second superlattice induced by the adjacent boron nitride layer. Therefore, twisted multilayer graphene systems offer us a fascinating field to explore two-dimensional ferroelectricity.