Giant ferroelectric polarization in a bilayer graphene heterostructure

At the interface of van der Waals heterostructures, the crystal symmetry and the electronic structure can be reconstructed, giving rise to physical properties superior to or absent in parent materials. Here by studying a Bernal bilayer graphene moire superlattice encapsulated by 30 degrees-twisted boron nitride flakes, we report an unprecedented ferroelectric polarization with the areal charge density up to 10(13)cm(-2), which is far beyond the capacity of a moire band. The translated polarization similar to 5 pCm(-1) is among the highest interfacial ferroelectrics engineered by artificially stacking van der Waals crystals. The gate-specific ferroelectricity and co-occurring anomalous screening are further visualized via Landau levels, and remain robust for Fermi surfaces outside moire bands, confirming their independence on correlated electrons. We also find that the gate-specific resistance hysteresis loops could be turned off by the other gate, providing an additional control knob. Furthermore, the ferroelectric switching can be applied to intrinsic properties such as topological valley current. Overall, the gate-specific ferroelectricity with strongly enhanced charge polarization may encourage more explorations to optimize and enrich this novel class of ferroelectricity, and promote device applications for ferroelectric switching of various quantum phenomena.

Automated summary

At the interface of van der Waals heterostructures, an unprecedented ferroelectric polarization has been observed in a Bernal bilayer graphene moire superlattice encapsulated by twisted boron nitride flakes. This ferroelectric polarization has a high charge density and can be controlled by adjusting the gate. Moreover, this ferroelectric switching can also be applied to other properties.