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arXiv 2103.15937cond-mat.mes-hall
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手性石墨烯纳米带的拓扑相变:从边带到端态

Topological phase transition in chiral graphene nanoribbons: from edge bands to end states

Jingcheng Li, Sofia Sanz, Nestor Merino-Díez, Manuel Vilas-Varela, Aran Garcia-Lekue, Martina Corso, Dimas G. de Oteyza, Thomas Frederiksen, Diego Peña, Jose Ignacio Pascual

摘要:

石墨烯纳米结构的尺寸和形状的精确控制允许工程自旋极化的边缘和拓扑状态,代表了一种新的来源,非传统的$π$磁性与量子自旋电子学的应用前景。它们出现的先决条件是存在强大的带隙相,这在扩展的石墨烯系统中很难找到:只有扶手椅型石墨烯纳米带(GNR)显示出带隙,然而,对于任何其他GNR取向都是封闭的。在这里,我们表明,半金属手征GNRs(chGNRs)缩小到纳米宽度经历了拓扑相变,成为第一个拓扑绝缘体,然后转化为平凡的带绝缘体的最后一个chGNRs。我们制作了原子精确的chGNRs不同的手性和大小的表面合成使用预先设计的分子前体。结合扫描隧道显微镜(STM)的测量和理论模拟,我们遵循的拓扑性质和体带隙的演变取决于宽度,长度和手性的chGNRs。第一个出现的间隙相是拓扑的,由边缘之间的手性相互作用模式保护。对于较窄的带状物,相互作用模式的对称性发生变化,拓扑能隙关闭并重新打开,作为一个平凡的带绝缘体。我们的研究结果代表了一个新的平台,产生拓扑保护的自旋态,并展示了连接手性边缘和缺陷结构与能带工程的潜力。

英文摘要:

Precise control over the size and shape of graphene nanostructures allows engineering spin-polarized edge and topological states, representing a novel source of non-conventional $π$-magnetism with promising applications in quantum spintronics. A prerequisite for their emergence is the existence of robust gapped phases, which are difficult to find in extended graphene systems: only armchair graphene nanoribbons (GNRs) show a band gap that, however, closes for any other GNR orientation. Here we show that semi-metallic chiral GNRs (chGNRs) narrowed down to nanometer widths undergoes a topological phase transition, becoming first topological insulators, and transforming then into trivial band insulators for the narrowest chGNRs. We fabricated atomically precise chGNRs of different chirality and size by on surface synthesis using predesigned molecular precursors. Combining scanning tunnelling microscopy (STM) measurements and theory simulations, we follow the evolution of topological properties and bulk band gap depending on the width, length, and chirality of chGNRs. The first emerging gapped phases are topological, protected by a chiral interaction pattern between edges. For narrower ribbons, the symmetry of the interaction pattern changes, and the topological gap closes and re-opens again as a trivial band insulator. Our findings represent a new platform for producing topologically protected spin states and demonstrates the potential of connecting chiral edge and defect structure with band engineering.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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