未扭转双层石墨烯中由图案化光产生的平带与拓扑弗洛凯微带
Flat and Topological Floquet Minibands from Patterned Light in Untwisted Bilayer Graphene
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中文总结 AI 辅助
研究提出用光印刻超晶格的替代方法，在未扭转双层石墨烯中产生平带与拓扑弗洛凯微带，该超晶格周期易调控，为构建相关相提供灵活平台。
中文摘要 AI 辅助
范德华材料中的二维超晶格具有平带和非平庸拓扑，最著名的是扭转双层石墨烯的所谓魔角处，此处的平带会产生关联相与拓扑相。然而这些超晶格通常通过扭转层或施加应变制造，样品制备完成后，其周期固定且极难调控。本文提出一种替代路径：利用图案化电磁场而非物理扭转或应变，通过光学方式印刻超晶格。我们表明，图案化的面内圆偏振光，以及由图案化的面外纵向场与均匀圆偏振场组成的组合驱动，会在AA堆叠和AB堆叠的双层石墨烯中产生孤立能带。在AB堆叠中，中心能带还会变得近乎平坦，捕获了驱动莫尔超晶格的关键特征。在该方法中，超晶格周期由光照设定，易于调控，且圆偏振光会破坏时间反演对称性。计算中心能带的谷陈数后，我们发现两种堆叠结构中都存在丰富的拓扑结构与多个相变。我们的结果确立了光诱导超晶格作为灵活且可调控的平台，用于在双层石墨烯中构建平带与拓扑相。
英文摘要
Two-dimensional superlattices in van der Waals materials host flat bands and nontrivial topology, most famously at the so-called magic angles of twisted bilayer graphene, where flat bands give rise to correlated and topological phases. Yet these superlattices are usually created by twisting the layers or applying strain, and once a sample is fabricated, their period is fixed and extremely difficult to tune. Here we propose an alternative route: imprint the superlattice optically, using patterned electromagnetic fields rather than a physical twist or strain. We show that patterned in-plane cir- cularly polarized light and a combined drive consisting of a patterned out-of-plane longitudinal field and a uniform circularly polarized field produce isolated bands in both AA- and AB-stacked bilayer graphene. In AB stacking, the central bands additionally become nearly flat, capturing key features of a driven moire superlattice. In this approach, the superlattice period is set by the illumination and is straightforward to tune, and circularly polarized light breaks time-reversal symmetry. Computing the valley Chern numbers of the central bands, we find a rich topological structure with several phase transitions in both stackings. Our results establish light-induced superlattices as a flexible and tunable platform for engineering flat bands and topological phases in bilayer graphene.
