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 structure1–5. 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 layers6. 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 transition7–9, resulting in a periodically modulated pseudo-magnetic field10–14, 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 state15–17. 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.

中文翻译：

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弯曲石墨烯超晶格中平坦带和相关状态的证据

二维原子晶体可以从根本上改变其性质，以响应外部影响，例如衬底取向或应变，形成具有新型电子结构的材料 1-5。一个例子是在双层石墨烯中创建弱色散的“平坦”带，用于两层取向之间的某些“神奇”扭曲角。这些平带中的淬灭动能促进了电子 - 电子相互作用并促进了强相关相的出现，例如超导性和相关绝缘体。然而，获得扭曲双层石墨烯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，我们提出了一种创建不涉及微调的平坦带的替代途径。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平坦衬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伪磁场 10-14，从而产生具有平坦电子带的“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坦带时，我们观察到状态密度中的赝隙状耗尽，这标志着相关状态的出现 15-17。二维晶体的这种屈曲为创建其他超晶格系统提供了一种策略，特别是用于探索平带特征的相互作用现象。