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Electromagnetic‐Dual Metasurfaces for Topological States along a 1D Interface
Laser & Photonics Reviews ( IF 11.0 ) Pub Date : 2019-08-14 , DOI: 10.1002/lpor.201900126
Dia'aaldin J. Bisharat 1 , Daniel F. Sievenpiper 1
Affiliation  

The discovery of topological insulators was rapidly followed by the advent of their photonic analogues, motivated by the prospect of backscattering‐immune light propagation. So far, however, implementations have mainly relied on engineering bulk modes in photonic crystals and waveguide arrays in two‐dimensional (2D) systems, which closely mimic their electronic counterparts. In addition, metamaterials‐based implementations subject to electromagnetic duality and bianisotropy conditions suffer from intricate designs and narrow operating bandwidths. Here, it is shown that symmetry‐protected topological states akin to the quantum spin‐Hall effect can be realized in a straightforward manner by coupling surface modes over metasurfaces of complementary electromagnetic responses. Specifically, stacking unit cells of such metasurfaces directly results in double Dirac cones of degenerate transverse‐electric (TE) and transverse‐magnetic (TM) modes, which break into a wide nontrivial bandgap at small interlayer separation. Consequently, the ultrathin structure supports robust gapless edge states, which are confined along a one‐dimensional (1D) line rather than a surface interface, as demonstrated at microwave frequencies by near‐field imaging. The simplicity and versatility of the proposed approach proves attractive as a tabletop platform for the study of classical topological phases, as well as for applications benefiting the compactness of metasurfaces and the potential of topological insulators.

中文翻译:

一维界面的拓扑状态的电磁双超表面

由于反向散射免疫光传播的前景,拓扑绝缘子的发现很快被其光子类似物的出现所推动。但是,到目前为止,实现主要依赖于二维(2D)系统中的光子晶体和波导阵列中的工程体模式,这些模式与电子副本非常相似。此外,受电磁双重性和各向异性影响的基于超材料的实现方式还具有复杂的设计和狭窄的工作带宽。在此表明,可以通过在互补电磁响应的超表面上耦合表面模式,以直接方式实现类似于量子自旋霍尔效应的对称保护拓扑状态。具体来说,这种超表面的单位晶胞的堆叠直接导致简并的横向电(TE)模式和横向磁(TM)模的双狄拉克锥,它们在较小的层间间隔处分裂成较宽的非平整带隙。因此,超薄结构支持稳健的无间隙边缘状态,该状态沿一维(1D)线而不是表面界面被限制,如在微波频率下通过近场成像所证明的那样。所提出的方法的简单性和多功能性被证明是作为研究经典拓扑阶段以及有益于超表面紧凑性和拓扑绝缘体潜力的应用的桌面平台的诱人之处。在较小的夹层间距下会分裂成很宽的非平整带隙。因此,超薄结构支持鲁棒的无间隙边缘状态,该状态沿一维(1D)线而不是表面界面被限制,如近场成像在微波频率下所证明的那样。所提出的方法的简单性和多功能性被证明是作为研究经典拓扑阶段以及有益于超表面紧凑性和拓扑绝缘体潜力的应用的桌面平台的诱人之处。在较小的夹层间距下会分裂成很宽的非平整带隙。因此,超薄结构支持稳健的无间隙边缘状态,该状态沿一维(1D)线而不是表面界面被限制,如近场成像在微波频率下所证明的那样。所提出的方法的简单性和多功能性被证明是作为研究经典拓扑阶段以及有益于超表面紧凑性和拓扑绝缘体潜力的应用的桌面平台的诱人之处。
更新日期:2019-08-14
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