Observation of unidirectional backscattering-immune topological electromagnetic states
Observation of unidirectional backscattering-immune topological electromagnetic states
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DOI：
10.1038/nature08293
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发表时间：
2009-10-08
期刊：
影响因子：
64.8
通讯作者：
Soljacic, Marin
中科院分区：
文献类型：
--
作者：
Wang, Zheng;Chong, Yidong;Soljacic, Marin
凝聚态物理学中最引人注目的现象之一是量子霍尔效应，它出现在二维电子系统(1-4)中，受到垂直于电子所在平面的大磁场的影响。在这种情况下，电流由电子沿着系统的边缘携带，处于所谓的手征边态(CES)。由于体电子能带结构的非平凡的拓扑性质，这些状态具有独特的方向性，并且对无序的散射是健壮的。最近，理论预测(5-7)可以在光子晶体中观察到这种电子边缘状态的电磁模拟，光子晶体是具有折射率变化的材料，其周期与通过它们的光的波长相当。本文报道了在微波条件下制作的磁光光子晶体(7)中这种电磁过程的实验实现和观测结果。我们证明，像它们的电子对应物(8-13)一样，电磁过程只能沿一个方向传播，并且对无序的散射非常健壮；我们发现，即使是放置在传播边缘模路径上的大型金属散射体也不会引起反射。这些模式可能会产生新类型的电磁设备和实验，而这是仅使用传统的倒易光子态是不可能的。此外，我们对光子过程的实验演示和研究为拓扑带理论在经典系统和玻色子系统中的推广和应用提供了强有力的支持，并可能导致拓扑现象的实现和观察，通常比电子系统更具可控性和可定制性。
One of the most striking phenomena in condensed-matter physics is the quantum Hall effect, which arises in two-dimensional electron systems(1-4) subject to a large magnetic field applied perpendicular to the plane in which the electrons reside. In such circumstances, current is carried by electrons along the edges of the system, in so-called chiral edge states (CESs). These are states that, as a consequence of nontrivial topological properties of the bulk electronic band structure, have a unique directionality and are robust against scattering from disorder. Recently, it was theoretically predicted(5-7) that electromagnetic analogues of such electronic edge states could be observed in photonic crystals, which are materials having refractive-index variations with a periodicity comparable to the wavelength of the light passing through them. Here we report the experimental realization and observation of such electromagnetic CESs in a magneto-optical photonic crystal(7) fabricated in the microwave regime. We demonstrate that, like their electronic counterparts(8-13), electromagnetic CESs can travel in only one direction and are very robust against scattering from disorder; we find that even large metallic scatterers placed in the path of the propagating edge modes do not induce reflections. These modes may enable the production of new classes of electromagnetic device and experiments that would be impossible using conventional reciprocal photonic states alone. Furthermore, our experimental demonstration and study of photonic CESs provides strong support for the generalization and application of topological band theories to classical and bosonic systems, and may lead to the realization and observation of topological phenomena in a generally much more controlled and customizable fashion than is typically possible with electronic systems.