双层石墨烯中AB-BA畴界及其新奇拓扑边界态的研究

Gapped graphene bilayer with smooth domain walls is predicted to be one of the most promising candidates where charge carriers can travel long distances without dissipation. The domain wall separating two opposite biased bilayer graphene is first proposed by Martin et al. to host one-dimensional (1D) topological states. Later, the domain wall between AB- and BA-stacked bilayer graphene under a uniform external field is demonstrated to be equivalent to the gate-polarity domain wall and it is believed to be a crystalline topological defect hosting topological gapless mode because of a change in the Chern number. The AB-BA domain wall in graphene bilayer, with electrons residing right at the surface, provides unprecedented opportunities to directly image the topologically protected 1D conducting channels. More importantly, such a crystalline topological line defect exists naturally in Bernal graphene bilayers grown by chemical vapor deposition and in exfoliated bilayer graphene (that is, prepared using adhesive tape) from graphite. In this project, we will direct characterize the structure of the AB-BA domain walls by using scanning tunneling microscope (STM) and tip-enhanced Raman spectroscopy. We will also study its topological edge states by using both scanning tunneling spectroscopy (STS) spectra and tip-enhanced Raman spectroscopy spectra.

寻找具有拓扑保护边界态的材料体系是凝聚态物理和材料物理的前沿研究热点，这些拓扑边界态在传输载流子时具有极低的耗散，在未来电子学器件中有巨大的应用前景。理论计算表明双层石墨烯的AB-BA畴界就能提供这样的拓扑边界态，最新的输运测量实验证实了这一预言。在本项目的支持下，我们将首次利用扫描隧道显微镜技术和针尖增强拉曼技术对双层石墨烯的AB-BA畴界进行系统研究，测量该体系的原子结构及畴界附近的针尖增强拉曼信号，并通过扫描隧道谱研究该体系的拓扑边界态及其在磁场、缺陷、吸附原子等的影响下的行为。本课题的研究将深入理解石墨烯量子体系中新奇拓扑边界态的行为，实现基于石墨烯的各种低能耗的功能电子器件，为石墨烯在未来微纳电子器件中的应用提供实验和理论上的支持。

寻找具有拓扑保护边界态的材料体系是凝聚态物理和材料物理的前沿研究热点，这些拓扑边界态在传输载流子时具有极低的耗散，在未来电子学器件中有巨大的应用前景。双层石墨烯的AB-BA畴界和小转角双层石墨烯的AB-BA畴界就能提供这样的拓扑边界态。在本项目的支持下，我们利用扫描隧道显微镜技术对双层石墨烯的AB-BA畴界和小转角双层石墨烯的AB-BA畴界进行了系统研究，测量该体系的原子结构及局域应变，并通过扫描隧道谱研究该体系的拓扑边界态及其在磁场的影响下的行为。进一步，我们发现利用STM针尖脉冲可对魔角双层石墨烯的AB-BA畴界网络进行调控，从而开关其二维导电拓扑网格。在本项目的支持下，何林课题组发表了39篇高水平研究成果，包括6篇PRL，2篇ACS Nano，1篇Nano Lett，1篇Science Bulletin，和二十余篇PRB。本课题的研究能帮助研究人员深入理解石墨烯量子体系中新奇拓扑边界态的行为。