Evidence of flat bands and correlated states in buckled graphene superlattices
Evidence of flat bands and correlated states in buckled graphene superlattices
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DOI：
10.1038/s41586-020-2567-3
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发表时间：
2020-08-13
期刊：
影响因子：
64.8
通讯作者：
Andrei, Eva Y.
中科院分区：
文献类型：
--
作者：
Mao, Jinhai;Milovanovic, Slavisa P.;Andrei, Eva Y.
二维原子晶体可以根据外部影响（例如基板取向或应变）从根本上改变其特性，从而形成具有新颖电子结构的材料(1-5)。一个例子是在双层石墨烯中创建弱色散的“平坦”带，以实现两层取向之间的某些“神奇”扭曲角(6)。这些平带中的淬灭动能促进电子-电子相互作用，并促进强相关相的出现，例如超导性和相关绝缘体。然而，在扭曲双层石墨烯中获得魔角所需的非常精确的微调对制造和可扩展性提出了挑战。在这里，我们提出了另一种创建平坦带的方法，不涉及微调。使用扫描隧道显微镜和光谱学以及数值模拟，我们证明放置在原子级平坦基底上的石墨烯单层可以被迫经历屈曲转变（7-9），从而产生周期性调制的赝磁场（10-14），从而创建具有平坦电子带的“后石墨烯”材料。当我们使用静电掺杂将费米能级引入这些平带时，我们观察到态密度中出现类似赝能隙的耗尽，这标志着相关态的出现(15-17)。二维晶体的屈曲为创建其他超晶格系统提供了一种策略，特别是探索平带特征的相互作用现象。人们发现屈曲单层石墨烯超晶格为扭曲双层石墨烯提供了替代方案，用于研究碳基材料中的平带和相关态。
Two-dimensional atomic crystals can radically change their properties in response to external influences, such as substrate orientation or strain, forming materials with novel electronic structure(1-5). An example is the creation of weakly dispersive, 'flat' bands in bilayer graphene for certain 'magic' angles of twist between the orientations of the two layers(6). The quenched kinetic energy in these flat bands promotes electron-electron interactions and facilitates the emergence of strongly correlated phases, such as superconductivity and correlated insulators. However, the very accurate fine-tuning required to obtain the magic angle in twisted-bilayer graphene poses challenges to fabrication and scalability. Here we present an alternative route to creating flat bands that does not involve fine-tuning. Using scanning tunnelling microscopy and spectroscopy, together with numerical simulations, we demonstrate that graphene monolayers placed on an atomically flat substrate can be forced to undergo a buckling transition(7-9), resulting in a periodically modulated pseudo-magnetic field(10-14), which in turn creates a 'post-graphene' material with flat electronic bands. When we introduce the Fermi level into these flat bands using electrostatic doping, we observe a pseudogap-like depletion in the density of states, which signals the emergence of a correlated state(15-17). This buckling of two-dimensional crystals offers a strategy for creating other superlattice systems and, in particular, for exploring interaction phenomena characteristic of flat bands.Buckled monolayer graphene superlattices are found to provide an alternative to twisted bilayer graphene for the study of flat bands and correlated states in a carbon-based material.