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Cloning of Dirac fermions in graphene superlattices

机译：石墨烯超晶格中狄拉克费米子的克隆

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Superlattices have attracted great interest because their use may make it possible to modify the spectra of two-dimensional electron systems and, ultimately, create materials with tailored electronic properties. In previous studies (see, for example, refs 1-8), it proved difficult to realize superlattices with short periodicities and weak disorder, and most of their observed features could be explained in terms of cyclotron orbits commensurate with the superlattice. Evidence for the formation of superlattice mini-bands (forming a fractal spectrum known as Hofstadter's butterfly9) has been limited to the observation of new low-field oscillations and an internal structure within Landau levels. Here we report transport properties of graphene placed on a boron nitride substrate and accurately aligned along its crystallographic directions. The substrate's moire potential acts as a superlattice and leads to profound changes in the graphene's electronic spectrum. Second-generation Dirac points appear as pronounced peaks in resistivity, accompanied by reversal of the Hall effect. The latter indicates that the effective sign of the charge carriers changes within graphene's conduction and valence bands. Strong magnetic fields lead to Zak-type cloning of the third generation of Dirac points, which are observed as numerous neutrality points in fields where a unit fraction of the flux quantum pierces the superlattice unit cell. Graphene superlattices such as this one provide a way of studying the rich physics expected in incommensurable quantum systems and illustrate the possibility of controllably modifying the electronic spectra of two-dimensional atomic crystals by varying their crystallographic alignment within van der Waals heterostuctures.
机译：超晶格引起了极大的兴趣，因为它们的使用可能使修改二维电子系统的光谱成为可能，并最终创建具有定制电子特性的材料。在以前的研究中（例如，参见参考文献1-8），很难实现具有短周期和弱无序性的超晶格，并且它们的大部分观测特征可以用与超晶格相对应的回旋轨道来解释。形成超晶格微带的证据（形成称为霍夫施塔特蝴蝶9的分形谱）仅限于观察新的低场振荡和朗道内的内部结构。在这里，我们报告了放置在氮化硼衬底上并沿着其晶体学方向精确排列的石墨烯的传输特性。基板的莫尔电位可作为超晶格，并导致石墨烯电子光谱发生深刻变化。第二代狄拉克点显示为电阻率的明显峰值，伴随着霍尔效应的逆转。后者表明电荷载流子的有效符号在石墨烯的导带和价带内变化。强磁场导致第三代狄拉克点的Zak型克隆，这在磁场中被视为众多中性点，在该场中，通量量子的单位分数刺穿了超晶格晶胞。诸如此类的石墨烯超晶格提供了一种研究无法估量的量子系统中预期的丰富物理的方法，并说明了通过改变范德华异质结构内的二维原子排列来可控地修改二维原子晶体电子光谱的可能性。

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  • 来源
    《Nature》 |2013年第7451期|594-597|共4页
  • 作者

    L. A. Ponomarenko; R. V. Gorbachev; G. L. Yu; D. C. Elias; R. Jalil; A. A. Patel; A. Mishchenko; A. S. Mayorov; C. R. Woods; J. R. Wallbank; M. Mucha-Kruczynski; B. A. Piot; M. Potemski; I. V. Grigorieva; K. S. Novoselov; F. Guinea; V. I. Falko; A. K. Geim;

  • 作者单位

    School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK;

    Centrefor Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, UK;

    School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK;

    School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK;

    Centrefor Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, UK;

    Physics Department, Lancaster University, Lancaster LA 14YB, UK;

    School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK;

    School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK;

    School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK;

    Physics Department, Lancaster University, Lancaster LA 14YB, UK;

    Physics Department, Lancaster University, Lancaster LA 14YB, UK;

    Laboratoire National des Champs Magnetiques Intenses.CNRS-UJF-UPS-INSA, F-38042 Grenoble, France;

    Laboratoire National des Champs Magnetiques Intenses.CNRS-UJF-UPS-INSA, F-38042 Grenoble, France;

    School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK;

    School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK;

    lnstituto de Ciencia de Materiales de Madrid, Sor Juana Ines de la Cruz 3, Madrid 28049, Spain;

    Physics Department, Lancaster University, Lancaster LA 14YB, UK;

    School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK,Centrefor Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, UK;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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