Moiré superlattices in two-dimensional van der Waals heterostructures provide an efficient way to engineer electron band properties. The recent discovery of exotic quantum phases and their interplay in twisted bilayer graphene (tBLG) has made this moiré system one of the most renowned condensed matter platforms. So far studies of tBLG have been mostly focused on the lowest two flat moiré bands at the first magic angle θ_m1 ∼ 1.1°, leaving high-order moiré bands and magic angles largely unexplored. Here we report an observation of multiple well-isolated flat moiré bands in tBLG close to the second magic angle θ_m2 ∼ 0.5°, which cannot be explained without considering electron–election interactions. With high magnetic field magnetotransport measurements we further reveal an energetically unbound Hofstadter butterfly spectrum in which continuously extended quantized Landau level gaps cross all trivial band gaps. The connected Hofstadter butterfly strongly evidences the topologically nontrivial textures of the multiple moiré bands. Overall, our work provides a perspective for understanding the quantum phases in tBLG and the fractal Hofstadter spectra of multiple topological bands.

二维范德华异质结构中的莫尔超晶格提供了一种设计电子能带特性的有效方法。最近发现的奇异量子相及其在扭曲双层石墨烯 (tBLG) 中的相互作用使这种莫尔系统成为最著名的凝聚态平台之一。到目前为止，对 tBLG 的研究主要集中在第一魔角 θ _m1 ∼ 1.1° 处最低的两个平坦莫尔带上，而高阶莫尔带和魔角在很大程度上未被探索。在这里，我们报告了在接近第二魔角 θ _{m2的 tBLG 中观察到多个良好隔离的平坦莫尔带}∼ 0.5°，如果不考虑电子 - 电子相互作用就无法解释。通过高磁场磁输运测量，我们进一步揭示了一个能量未绑定的 Hofstadter 蝴蝶谱，其中连续扩展的量化朗道能级间隙跨越所有微不足道的带隙。连接的 Hofstadter 蝴蝶有力地证明了多个莫尔条纹的拓扑非平凡纹理。总的来说，我们的工作为理解 tBLG 中的量子相和多个拓扑带的分形 Hofstadter 光谱提供了一个视角。