Letter

Unconventional quantum Hall effect and Berry’s phase of 2π in bilayer graphene

Received:
Accepted:
Published online:

Abstract

There are two known distinct types of the integer quantum Hall effect. One is the conventional quantum Hall effect, characteristic of two-dimensional semiconductor systems1,2, and the other is its relativistic counterpart observed in graphene, where charge carriers mimic Dirac fermions characterized by Berry’s phase π, which results in shifted positions of the Hall plateaus3,4,5,6,7,8,9. Here we report a third type of the integer quantum Hall effect. Charge carriers in bilayer graphene have a parabolic energy spectrum but are chiral and show Berry’s phase 2π affecting their quantum dynamics. The Landau quantization of these fermions results in plateaus in Hall conductivity at standard integer positions, but the last (zero-level) plateau is missing. The zero-level anomaly is accompanied by metallic conductivity in the limit of low concentrations and high magnetic fields, in stark contrast to the conventional, insulating behaviour in this regime. The revealed chiral fermions have no known analogues and present an intriguing case for quantum-mechanical studies.

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Acknowledgements

We thank the High Field Magnet Laboratory (Nijmegen) for their hospitality. U.Z. and K.S.N. were partially supported by EuroMagNET of the 6th Framework ‘Structuring the European Research Area, Research Infrastructures Action’ and by the Leverhulme Trust. S.V.M. acknowledges support from the Russian Academy of Sciences. This research was funded by the EPSRC (UK).

Author information

Affiliations

  1. Manchester Centre for Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, UK

    • K. S. Novoselov
    • , S. V. Morozov
    • , D. Jiang
    • , F. Schedin
    •  & A. K. Geim
  2. Department of Physics, Lancaster University, Lancaster LA1 4YB, UK

    • E. McCann
    •  & V. I. Fal’ko
  3. Institute for Microelectronics Technology, 142432 Chernogolovka, Russia

    • S. V. Morozov
  4. Institute for Molecules and Materials, Radboud University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands

    • M. I. Katsnelson
    •  & U. Zeitler

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Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to A. K. Geim.

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