Emergent ferroelectrics in 2D moiré superlattices

DIPC Seminars

Qiong Ma
Boston College
Donostia International Physics Center
Maia Vergniory
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Emergent ferroelectrics in 2D moiré superlattices

Discovering and understanding emergent phenomena in quantum materials—especially in which multiple degrees of freedom or energy scales are delicately balanced—is of fundamental interest to condensed-matter research. Here we report on the surprising observation of emergent ferroelectricity in graphene-based moiré heterostructures. Ferroelectric materials show electrically switchable electric dipoles, usually formed by spatial separation between the average positive and negative charge centers within the unit cell. On this basis, it is difficult to imagine graphene—a material composed of only carbon atoms—exhibiting ferroelectricity. However, in this work, we realize switchable ferroelectricity in Bernal-stacked bilayer graphene sandwiched between two hexagonal boron nitride layers. By introducing a moiré superlattice potential (via aligning bilayer graphene with the top and/or bottom boron nitride crystals), we observe prominent and robust hysteretic behavior of the graphene resistance with an externally applied out-of-plane displacement field. Our systematic transport measurements reveal a rich and striking response as a function of the displacement field and electron filling and beyond the framework of conventional ferroelectrics. This emergent moiré ferroelectricity may enable ultrafast, programmable, and atomically thin carbon-based memory devices.