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Observation of unconventional edge states in ‘photonic graphene’

Nature Materials volume 13, pages 57–62 (2014)Cite this article

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Abstract

Graphene, a two-dimensional honeycomb lattice of carbon atoms, has been attracting much interest in recent years. Electrons therein behave as massless relativistic particles, giving rise to strikingly unconventional phenomena. Graphene edge states are essential for understanding the electronic properties of this material. However, the coarse or impure nature of the graphene edges hampers the ability to directly probe the edge states. Perhaps the best example is given by the edge states on the bearded edge that have never been observed—because such an edge is unstable in graphene. Here, we use the optical equivalent of graphene—a photonic honeycomb lattice—to study the edge states and their properties. We directly image the edge states on both the zigzag and bearded edges of this photonic graphene, measure their dispersion properties, and most importantly, find a new type of edge state: one residing on the bearded edge that has never been predicted or observed. This edge state lies near the Van Hove singularity in the edge band structure and can be classified as a Tamm-like state lacking any surface defect. The mechanism underlying its formation may counterintuitively appear in other crystalline systems.

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Figure 1: Physical structure and band structure of photonic honeycomb lattices.
Figure 2: Experimental demonstration of an edge state at the zigzag edge of an optically induced honeycomb lattice.
Figure 3: Momentum-resolved measurements of edge states in a photonic honeycomb lattice.
Figure 4: Calculating the new edge state.

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Acknowledgements

The Technion team is part of the Israeli Center of Research Excellence ‘Circle of Light’ supported by the I-CORE Program of the Planning and Budgeting Committee and The Israel Science Foundation. M.C.R. is grateful to the Azrieli foundation for the Azrieli fellowship. This research was financially supported by an Advanced Grant from the European Research Council; the Israel Science Foundation; the USA-Israel Binational Science Foundation; the German Ministry of Education and Science (ZIK 03Z1HN31); the 973 Programs (2013CB328702, 2013CB632703) and the Program for Changjiang Scholars and Innovative Research Teams in China; and by the NSF and AFOSR in the USA.

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Author notes

  1. Yonatan Plotnik, Mikael C. Rechtsman and Daohong Song: These authors contributed equally to this work

Authors and Affiliations

  1. Technion—Israel Institute of Technology, Technion City 32000, Haifa, Israel

    Yonatan Plotnik, Mikael C. Rechtsman, Yaakov Lumer & Mordechai Segev

  2. The MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Applied Physical School and School of Physics, Nankai University, Tianjin 300457, China

    Daohong Song, Jingjun Xu & Zhigang Chen

  3. Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany

    Matthias Heinrich, Julia M. Zeuner, Stefan Nolte & Alexander Szameit

  4. Department of Physics and Astronomy, San Francisco State University, San Francisco, California 94132, USA

    Natalia Malkova & Zhigang Chen

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  1. Yonatan Plotnik
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All authors contributed significantly to this work.

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Correspondence to Mordechai Segev.

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Plotnik, Y., Rechtsman, M., Song, D. et al. Observation of unconventional edge states in ‘photonic graphene’. Nature Mater 13, 57–62 (2014). https://doi.org/10.1038/nmat3783

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