Zhang Le, Ding Jing, Xiang Hanxiao, Liu Naitian, Zhou Wenqiang, Wu Linfeng, Xin Na, Watanabe Kenji, Taniguchi Takashi, Xu Shuigang
Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China.
Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China.
Nat Commun. 2024 Dec 30;15(1):10905. doi: 10.1038/s41467-024-55281-z.
Extending ferroelectric materials to two-dimensional limit provides versatile applications for the development of next-generation nonvolatile devices. Conventional ferroelectricity requires materials consisting of at least two constituent elements associated with polar crystalline structures. Monolayer graphene as an elementary two-dimensional material unlikely exhibits ferroelectric order due to its highly centrosymmetric hexagonal lattices. Here, we report the observations of electronic ferroelectricity in monolayer graphene by introducing asymmetric moiré superlattice at the graphene/h-BN interface, in which the electric polarization stems from electron-hole dipoles. The polarization switching is probed through the measurements of itinerant Hall carrier density up to room temperature, manifesting as standard polarization-electric field hysteresis loops. We find ferroelectricity in graphene moiré systems exhibits generally similar characteristics in monolayer, bilayer, and trilayer graphene, which indicates layer polarization is not essential to observe the ferroelectricity. Furthermore, we demonstrate the applications of this ferroelectric moiré structures in multi-state nonvolatile data storage with high retention and the emulation of versatile synaptic behaviors. Our work not only provides insights into the fundamental understanding of ferroelectricity, but also demonstrates the potential of graphene for high-speed and multi-state nonvolatile memory applications.
将铁电材料扩展到二维极限为下一代非易失性器件的发展提供了广泛的应用。传统铁电性要求材料由至少两种与极性晶体结构相关的组成元素构成。作为一种基本的二维材料，单层石墨烯由于其高度中心对称的六边形晶格，不太可能表现出铁电有序性。在此，我们报告了通过在石墨烯/h-BN界面引入不对称莫尔超晶格，在单层石墨烯中观测到电子铁电性，其中电极化源于电子-空穴偶极子。通过测量直至室温的巡游霍尔载流子密度来探测极化切换，表现为标准的极化-电场滞后回线。我们发现石墨烯莫尔系统中的铁电性在单层、双层和三层石墨烯中通常表现出相似的特性，这表明层极化对于观测铁电性并非必不可少。此外，我们展示了这种铁电莫尔结构在具有高保持性的多态非易失性数据存储以及通用突触行为模拟中的应用。我们的工作不仅为铁电性的基本理解提供了见解，还展示了石墨烯在高速和多态非易失性存储器应用中的潜力。
