title: Observation of unconventional edge states in 'photonic graphene'.
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.
authors.affiliation: 1] Technion-Israel Institute of Technology, Technion City 32000, Haifa, Israel [2].
authors.forename: Yonatan
authors.initials: Y
authors.lastname: Plotnik
authors.affiliation: 1] Technion-Israel Institute of Technology, Technion City 32000, Haifa, Israel [2].
authors.forename: Mikael C
authors.initials: MC
authors.lastname: Rechtsman
authors.affiliation: 1] The MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Applied Physical School and School of Physics, Nankai University, Tianjin 300457, China [2].
authors.forename: Daohong
authors.initials: D
authors.lastname: Song
authors.affiliation: Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Heinrich
authors.affiliation: Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany.
authors.forename: Julia M
authors.initials: JM
authors.lastname: Zeuner
authors.affiliation: Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Nolte
authors.affiliation: Technion-Israel Institute of Technology, Technion City 32000, Haifa, Israel.
authors.forename: Yaakov
authors.initials: Y
authors.lastname: Lumer
authors.affiliation: Department of Physics and Astronomy, San Francisco State University, San Francisco, California 94132, USA.
authors.forename: Natalia
authors.initials: N
authors.lastname: Malkova
authors.affiliation: The MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Applied Physical School and School of Physics, Nankai University, Tianjin 300457, China.
authors.forename: Jingjun
authors.initials: J
authors.lastname: Xu
authors.affiliation: Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Szameit
authors.affiliation: 1] The MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Applied Physical School and School of Physics, Nankai University, Tianjin 300457, China [2] Department of Physics and Astronomy, San Francisco State University, San Francisco, California 94132, USA.
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Technion-Israel Institute of Technology, Technion City 32000, Haifa, Israel.
authors.forename: Mordechai
authors.initials: M
authors.lastname: Segev