The design and fabrication of robust metallic states in graphene nanoribbons (GNRs) are challenging because lateral quantum confinement and many-electron interactions induce electronic band gaps when graphene is patterned at nanometer length scales. Recent developments in bottom-up synthesis have enabled the design and characterization of atomically precise GNRs, but strategies for realizing GNR metallicity have been elusive. Here we demonstrate a general technique for inducing metallicity in GNRs by inserting a symmetric superlattice of zero-energy modes into otherwise semiconducting GNRs. We verify the resulting metallicity using scanning tunneling spectroscopy as well as first-principles density-functional theory and tight-binding calculations. Our results reveal that the metallic bandwidth in GNRs can be tuned over a wide range by controlling the overlap of zero-mode wave functions through intentional sublattice symmetry breaking.

石墨烯纳米带（GNR）中坚固的金属态的设计和制造具有挑战性，因为当石墨烯在纳米长度尺度上图案化时，横向量子限制和多电子相互作用会引起电子带隙。自下而上合成的最新进展使原子精确的GNR设计和表征成为可能，但是实现GNR金属性的策略却难以捉摸。在这里，我们通过将零能量模式的对称超晶格插入否则为半导体的GNR中，展示了一种用于在GNR中诱导金属性的通用技术。我们使用扫描隧道光谱以及第一原理密度泛函理论和紧密结合计算来验证所得的金属性。