Moiré Patterns in Domain Structures of Twisted Ferroelectric Bilayers

Twisting two layers of graphene by a magic angle has given rise to emergent microstructures and material properties such as unconventional superconductivity. Here, we predict the emergence of moiré patterns in the domain structure of twisted ferroelectric BaTiO₃ bilayers of nanometer thickness using phase-field simulations incorporating the Landau theory of ferroelectrics. We find that regular domain structures with excellent two-dimensional periodicity can spontaneously form when the two layers both containing original one-dimensional stripe domains are twisted by 30° , showing a mesoscale moiré pattern of ferroelectric domain walls. This superstructure has eight degenerate variants that can be achieved by tuning the initial poling field and these variants may coexist to assemble into more complicated polar textures. Additionally, transition between degenerate states by applying external fields is demonstrated. This computational discovery of novel domain structures opens up new avenues for nanoelectronics and twistronics based on twisted ferroelectric bilayers.