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Unconventional ferroelectricity in moire heterostructures

机译：Moire异质结构的非传统铁电性

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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 research(1,2). Here we report on the surprising observation of emergent ferroelectricity in graphene-based moire 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 ferroelectricity(3). However, in this work we realize switchable ferroelectricity in Bernal-stacked bilayer graphene sandwiched between two hexagonal boron nitride layers. By introducing a moire 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 moire system. This emergent moire ferroelectricity may enable ultrafast, programmable and atomically thin carbon-based memory devices.Electronic ferroelectricity is observed in a graphene-based moire heterostructure, which is explained using a spontaneous interlayer charge-transfer model driven by layer-specific on-site Coulomb repulsion.
机译：物质的组成颗粒可以以各种方式安排自己，从而产生可能令人惊讶的现象，并且通常不能通过研究个体成分来理解。发现和理解量子材料中这种现象的出现 - 尤其是那些多程度的自由度或能量尺度的精致性均衡 - 对凝聚物研究的基本兴趣（1,2）。在这里，我们报告了基于石墨烯的莫雷异质结构中的紧急铁电性的令人惊讶的观察。铁电材料显示出电切换电偶极子，其通常通过在单元电池内的平均正和负电荷的平均中心之间的空间分离形成。在此基础上，难以想象石墨烯 - 仅由碳原子呈现铁电性（3）组成的材料。然而，在这项工作中，我们在夹在两个六边形氮化硼层之间的伯尼堆叠双层石墨烯中实现可切换的铁电性。通过引入Moire超晶格电位（通过与顶部和/或底部氮化硼晶体的双层石墨烯对准），我们观察到具有外部施加的外平移场的石墨烯抗性的突出和稳健的滞后行为。我们的系统运输测量揭示了富有的尖锐响应，作为位移场和电子填充的功能，以及超出传统铁电的框架。我们进一步直接通过非局部单层石墨烯传感器探测铁电偏振。我们的结果表明了双层石墨烯/氮化硼莫尔系统中的非常规，奇数奇偶校验电子订购。这种紧急的莫尔铁电性可以使超快，可编程和原子薄的碳基存储器件能够在基于石墨烯的莫尔异质结构中观察到电子铁电性，其使用由特定于层现场库仑驱动的自发层间电荷转移模型来解释排斥。

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  • 来源
    《Nature》 |2020年第7836期|71-76|共6页
  • 作者

    Zheng Zhiren; Ma Qiong; Bi Zhen; de la Barrera Sergio; Liu Ming-Hao; Mao Nannan; Zhang Yang; Kiper Natasha; Watanabe Kenji; Taniguchi Takashi; Kong Jing; Tisdale William A.; Ashoori Ray; Gedik Nuh; Fu Liang; Xu Su-Yang; Jarillo-Herrero Pablo;

  • 作者单位

    MIT Dept Phys Cambridge MA 02139 USA;

    MIT Dept Phys Cambridge MA 02139 USA|Boston Coll Dept Phys Chestnut Hill MA 02167 USA;

    MIT Dept Phys Cambridge MA 02139 USA;

    MIT Dept Phys Cambridge MA 02139 USA;

    Natl Cheng Kung Univ Dept Phys Tainan Taiwan;

    MIT Dept Elect Engn & Comp Sci Cambridge MA 02139 USA|MIT Dept Chem Engn Cambridge MA 02139 USA;

    MIT Dept Phys Cambridge MA 02139 USA;

    MIT Dept Phys Cambridge MA 02139 USA;

    Natl Inst Mat Sci Res Ctr Funct Mat Tsukuba Ibaraki Japan;

    Natl Inst Mat Sci Int Ctr Mat Nanoarchitecton Tsukuba Ibaraki Japan;

    MIT Dept Elect Engn & Comp Sci Cambridge MA 02139 USA;

    MIT Dept Chem Engn Cambridge MA 02139 USA;

    MIT Dept Phys Cambridge MA 02139 USA;

    MIT Dept Phys Cambridge MA 02139 USA;

    MIT Dept Phys Cambridge MA 02139 USA;

    MIT Dept Phys Cambridge MA 02139 USA|Harvard Univ Dept Chem & Chem Biol Cambridge MA 02138 USA;

    MIT Dept Phys Cambridge MA 02139 USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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