Observation of unconventional edge states in 'photonic graphene'
Observation of unconventional edge states in 'photonic graphene'
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DOI：
10.1038/nmat3783
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发表时间：
2014-01-01
期刊：
影响因子：
41.2
通讯作者：
Segev, Mordechai
中科院分区：
文献类型：
--
作者：
Plotnik, Yonatan;Rechtsman, Mikael C.;Segev, Mordechai
石墨烯是碳原子的二维蜂窝状晶格，近年来引起了人们的极大兴趣。其中的电子表现为无质量的相对论性粒子，产生了引人注目的非常规现象。石墨烯的边缘状态对于理解这种材料的电子特性至关重要。然而，石墨烯边缘的粗糙或不纯性质阻碍了直接探测边缘状态的能力。也许最好的例子是从未被观察到的胡须边缘的边缘状态，因为这样的边缘在石墨烯中是不稳定的。在这里，我们使用石墨烯的光学等效物——光子蜂窝晶格——来研究边缘状态及其性质。我们直接对这种光子石墨烯的锯齿状边缘和胡须状边缘的边缘状态进行成像，测量它们的色散特性，最重要的是，发现了一种新的边缘状态：一种位于胡须状边缘的边缘状态，这种边缘状态从未被预测或观察过。这种边缘态位于边缘带结构中的Van Hove奇点附近，可以归类为没有任何表面缺陷的类tam态。它的形成机制可能与直觉相反地出现在其他晶体系统中。
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.