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Hierarchy of Hofstadter states and replica quantum Hall ferromagnetism in graphene superlattices

Nature Physics volume 10, pages 525–529 (2014)Cite this article

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An Erratum to this article was published on 30 September 2014

Abstract

Self-similarity and fractals have fascinated researchers across various disciplines. In graphene placed on boron nitride and subjected to a magnetic field, self-similarity appears in the form of numerous replicas of the original Dirac spectrum, and their quantization gives rise to a fractal pattern of Landau levels, referred to as the Hofstadter butterfly. Here we employ capacitance spectroscopy to probe directly the density of states (DoS) and energy gaps in this spectrum. Without a magnetic field, replica spectra are seen as pronounced DoS minima surrounded by van Hove singularities. The Hofstadter butterfly shows up as recurring Landau fan diagrams in high fields. Electron–electron interactions add another twist to the self-similar behaviour. We observe suppression of quantum Hall ferromagnetism, a reverse Stoner transition at commensurable fluxes and additional ferromagnetism within replica spectra. The strength and variety of the interaction effects indicate a large playground to study many-body physics in fractal Dirac systems.

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Figure 1: Capacitance spectroscopy of graphene superlattices.
Figure 2: Magnetocapacitance oscillations and quantized density of states.
Figure 3: Hofstadter butterfly in graphene superlattices.
Figure 4: Interactions in Hofstadter minibands.

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Acknowledgements

This work was supported by the European Research Council, the Royal Society, Graphene Flagship, Science and Innovation Award from the EPSRC (UK) and EuroMagNET II (EU Contract 228043).

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Authors and Affiliations

  1. School of Physics & Astronomy, University of Manchester, Manchester M13 9PL, UK

    G. L. Yu, L. A. Ponomarenko, D. C. Elias, I. V. Grigorieva, K. S. Novoselov, A. K. Geim & A. Mishchenko

  2. Centre for Mesoscience & Nanotechnology, University of Manchester, Manchester M13 9PL, UK

    R. V. Gorbachev, J. S. Tu, A. V. Kretinin, Y. Cao, R. Jalil, F. Withers & A. K. Geim

  3. Physics Department, Lancaster University, LA1 4YB, UK

    L. A. Ponomarenko, X. Chen & V. I. Fal’ko

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

    B. A. Piot & M. Potemski

  5. Departamento de Física, Universidade Federal de Minas Gerais, 30123-970, Belo Horizonte, Brazil

    D. C. Elias

  6. National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan

    K. Watanabe & T. Taniguchi

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Contributions

J.S.T., A.V.K., Y.C., R.J. and F.W. designed and fabricated the devices. A.M. and G.L.Y. carried out the measurements. B.A.P. and M.P. helped with high-field experiments. X.C. and V.I.F. provided theoretical support. K.W. and T.T. provided hBN crystals. R.V.G. devised the fabrication technology for graphene capacitors. A.M. developed the on-chip capacitance bridge. A.M., V.I.F. and A.K.G. analysed the results. A.K.G. together with V.I.F. wrote the manuscript. K.S.N., I.V.G., L.A.P. and D.C.E. helped with experiments and/or writing the paper. Section 4 of the Supplementary Information was written by V.I.F. All authors contributed to discussions.

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Correspondence to V. I. Fal’ko, A. K. Geim or A. Mishchenko.

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The authors declare no competing financial interests.

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Yu, G., Gorbachev, R., Tu, J. et al. Hierarchy of Hofstadter states and replica quantum Hall ferromagnetism in graphene superlattices. Nature Phys 10, 525–529 (2014). https://doi.org/10.1038/nphys2979

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