The ability to manipulate electrons in two-dimensional materials with external electric fields provides a route to synthetic band engineering. By imposing artificially designed and spatially periodic superlattice potentials, electronic properties can be further altered beyond the constraints of naturally occurring atomic crystals^1,2,3,4,5. Here, we report a new approach to fabricate high-mobility superlattice devices by integrating surface dielectric patterning with atomically thin van der Waals materials. By separating the device assembly and superlattice fabrication processes, we address the intractable trade-off between device processing and mobility degradation that constrains superlattice engineering in conventional systems. The improved electrostatics of atomically thin materials allows smaller wavelength superlattice patterns relative to previous demonstrations. Moreover, we observe the formation of replica Dirac cones in ballistic graphene devices with sub-40 nm wavelength superlattices and report fractal Hofstadter spectra^6,7,8 under large magnetic fields from superlattices with designed lattice symmetries that differ from that of the host crystal. Our results establish a robust and versatile technique for band structure engineering of graphene and related van der Waals materials with dynamic tunability.

利用外部电场操纵二维材料中的电子的能力为合成能带工程提供了一条途径。通过施加人工设计的和空间周期性的超晶格电势，可以进一步改变电子性质，使其超出天然存在的原子晶体^1,2,3,4,5的限制。。在这里，我们报告了一种通过将表面介电图案与原子上薄的范德华材料相集成来制造高迁移率超晶格器件的新方法。通过将器件组装和超晶格制造工艺分开，我们解决了器件加工与迁移率降低之间难以解决的折衷问题，这些折衷制约了常规系统中的超晶格工程。相对于先前的演示，原子薄材料的改进的静电允许较小的波长超晶格图案。此外，我们观察到了具有小于40 nm波长超晶格的弹道石墨烯器件中复制品狄拉克锥的形成，并报告了分形霍夫施塔特光谱^6,7,8在超晶格的大磁场作用下，其设计的晶格对称性不同于基质晶体的晶格对称性。我们的结果为具有动态可调性的石墨烯和相关范德华材料的能带结构工程建立了一种强大而通用的技术。