Unconventional ferroelectricity in moiré heterostructures

Zhiren Zheng, Qiong Ma (), Zhen Bi, Sergio Barrera, Ming-Hao Liu, Nannan Mao, Yang Zhang, Natasha Kiper, Kenji Watanabe, Takashi Taniguchi, Jing Kong, William A. Tisdale, Ray Ashoori, Nuh Gedik, Liang Fu, Su-Yang Xu and Pablo Jarillo-Herrero ()
Additional contact information
Zhiren Zheng: Massachusetts Institute of Technology
Qiong Ma: Massachusetts Institute of Technology
Zhen Bi: Massachusetts Institute of Technology
Sergio Barrera: Massachusetts Institute of Technology
Ming-Hao Liu: National Cheng Kung University
Nannan Mao: Massachusetts Institute of Technology
Yang Zhang: Massachusetts Institute of Technology
Natasha Kiper: Massachusetts Institute of Technology
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Jing Kong: Massachusetts Institute of Technology
William A. Tisdale: Massachusetts Institute of Technology
Ray Ashoori: Massachusetts Institute of Technology
Nuh Gedik: Massachusetts Institute of Technology
Liang Fu: Massachusetts Institute of Technology
Su-Yang Xu: Massachusetts Institute of Technology
Pablo Jarillo-Herrero: Massachusetts Institute of Technology

Nature, 2020, vol. 588, issue 7836, 71-76

Abstract: Abstract The constituent particles of matter can arrange themselves in various ways, giving rise to emergent phenomena that can be surprisingly rich and often cannot be understood by studying only the individual constituents. Discovering and understanding the emergence of such phenomena in quantum materials—especially those in which multiple degrees of freedom or energy scales are delicately balanced—is of fundamental interest to condensed-matter research1,2. Here we report on the surprising observation of emergent ferroelectricity in graphene-based moiré heterostructures. Ferroelectric materials show electrically switchable electric dipoles, which are usually formed by spatial separation between the average centres of positive and negative charge within the unit cell. On this basis, it is difficult to imagine graphene—a material composed of only carbon atoms—exhibiting ferroelectricity3. 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 behaviour 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 displacement field and electron filling, and beyond the framework of conventional ferroelectrics. We further directly probe the ferroelectric polarization through a non-local monolayer graphene sensor. Our results suggest an unconventional, odd-parity electronic ordering in the bilayer graphene/boron nitride moiré system. This emergent moiré ferroelectricity may enable ultrafast, programmable and atomically thin carbon-based memory devices.

Date: 2020
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DOI: 10.1038/s41586-020-2970-9

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