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Microscopic polarization in bilayer graphene

Nature Physics volume 7, pages 649–655 (2011)Cite this article

Abstract

Bilayer graphene contains, compared to single-layer graphene, additional states related to the symmetry of the layers. These states can lead to the opening of a bandgap, which is highly desirable for device applications. The gap can be either tunable through an external electric field or spontaneously formed through an interaction-induced symmetry breaking. Here, we report scanning tunnelling microscopy measurements that reveal that the microscopic nature of the bilayer gap is very different from what has been observed in previous macroscopic measurements, and from what is expected from current theoretical models. The potential difference between the layers, which is proportional to charge imbalance and determines the gap value, shows a strong dependence on the disorder potential and varies spatially in both magnitude and sign on a microscopic level. Additional interaction-induced effects are observed on applying a magnetic field, as a subgap opens once the zero-orbital Landau level is placed at the Fermi energy.

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Figure 1: Schematics of the bilayer graphene measurements and energy band diagrams in the quantum Hall regime.
Figure 2: STM topography images and disorder potential in bilayer graphene.
Figure 3: Magnetic quantization in bilayer graphene as a function of electric and magnetic fields.
Figure 4: Bilayer graphene potential energy asymmetries at varying gate voltage for electron and hole puddles.
Figure 5: Symmetry breaking in the LL(0,+);(1,+) quartet.

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Acknowledgements

We would like to acknowledge M. Stiles, S. Adam, H. Min, A. H. MacDonald and L. Levitov for fruitful discussions and thank I. Calizo and A. Hight-Walker for Raman spectroscopy characterization of the graphene system.

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Author notes

  1. Gregory M. Rutter and Suyong Jung: These authors contributed equally to this work

Authors and Affiliations

  1. Center for Nanoscale Science and Technology, NIST, Gaithersburg, Maryland 20899, USA

    Gregory M. Rutter, Suyong Jung, Nikolai N. Klimov, Nikolai B. Zhitenev & Joseph A. Stroscio

  2. Maryland NanoCenter, University of Maryland, College Park, Maryland 20742, USA

    Suyong Jung & Nikolai N. Klimov

  3. Physical Measurement Laboratory, NIST, Gaithersburg, Maryland 20899, USA

    Nikolai N. Klimov & David B. Newell

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  1. Gregory M. Rutter
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Contributions

The graphene sample was fabricated by S.J. and N.N.K. STM/STS measurements were performed by G.M.R., S.J., N.N.K. and J.A.S. The data analysis and preparation of the manuscript were performed by G.M.R., S.J., J.A.S., D.B.N. and N.B.Z.

Corresponding authors

Correspondence to Nikolai B. Zhitenev or Joseph A. Stroscio.

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The authors declare no competing financial interests.

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Rutter, G., Jung, S., Klimov, N. et al. Microscopic polarization in bilayer graphene. Nature Phys 7, 649–655 (2011). https://doi.org/10.1038/nphys1988

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