Article

Plasmons in graphene moiré superlattices

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Abstract

Moiré patterns are periodic superlattice structures that appear when two crystals with a minor lattice mismatch are superimposed. A prominent recent example is that of monolayer graphene placed on a crystal of hexagonal boron nitride. As a result of the moiré pattern superlattice created by this stacking, the electronic band structure of graphene is radically altered, acquiring satellite sub-Dirac cones at the superlattice zone boundaries. To probe the dynamical response of the moiré graphene, we use infrared (IR) nano-imaging to explore propagation of surface plasmons, collective oscillations of electrons coupled to IR light. We show that interband transitions associated with the superlattice mini-bands in concert with free electrons in the Dirac bands produce two additive contributions to composite IR plasmons in graphene moiré superstructures. This novel form of collective modes is likely to be generic to other forms of moiré-forming superlattices, including van der Waals heterostructures.

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Acknowledgements

Work at the University of California, San Diego (UCSD), on optical phenomena in vdW materials is supported by DOE-BES DE-FG02-00ER45799. Research at UCSD on tunable plasmonic reflectors is supported by ONR. D.N.B. is funded by the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4533. The development of scanning plasmon interferometry is supported by DOE-BES and ARO. G.X.N., B.Ö. and A.H.C.N. acknowledge the National Research Foundation, Prime Minister Office, Singapore, under its Medium Sized Centre Program and CRP award ‘Novel 2D materials with tailored properties: beyond graphene’ (R-144-000-295-281).

Author information

Affiliations

  1. Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore

    • G. X. Ni
    • , B. Özyilmaz
    •  & A. H. Castro Neto
  2. Department of Physics, University of California, San Diego, La Jolla, California 92093, USA

    • G. X. Ni
    • , J. S. Wu
    • , Z. Fei
    • , M. D. Goldflam
    • , M. M. Fogler
    •  & D. N. Basov
  3. State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road Shanghai 200050, China

    • H. Wang
    •  & X. M. Xie
  4. Ludwig-Maximilians-Universität and Center for Nanoscience, 80539 München, Germany

    • F. Keilmann

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Contributions

All authors were involved in designing the research, performing the research, and writing the paper.

Competing interests

F.K. is one of the co-founders of Neaspec, producer of the s-SNOM apparatus used in this study.

Corresponding author

Correspondence to D. N. Basov.

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