Experimental observation of photonic nodal line degeneracies in metacrystals.
Experimental observation of photonic nodal line degeneracies in metacrystals.
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DOI：
10.1038/s41467-018-03407-5
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发表时间：
2018-03-05
影响因子：
16.6
通讯作者：
Zhang S
中科院分区：
文献类型：
--
作者：
Gao W;Yang B;Tremain B;Liu H;Guo Q;Xia L;Hibbins AP;Zhang S
节线半金属(NLS)是一种三维(3D)晶体，在布里渊区以一维环的形式支持能带交叉。在自旋-轨道耦合或晶体对称性降低的情况下，NLS可能转变为狄拉克半金属、Weyl半金属或三维拓扑绝缘体。在光子学的背景下，尽管实现了拓扑相，如Chern绝缘体、拓扑绝缘体、Weyl和Dirac简并，但到目前为止还没有关于光子节线(NLS)的实验演示的报道。在这里，我们实验地演示了具有工程设计的负体等离子体色散的微波切线准晶体中的NL简并。通过对扫描的近场分布进行空间傅里叶变换，观察到了NL超材料的体态和表面态。此外，我们还从理论上证明了在偏晶设计中引入陀螺材料后，NL简并度可以转化为两个Weyl点。我们的发现可能会启发拓扑光子学的进一步发展。节线是在布里渊区形成一个环的一维能带交叉点，可以产生Weyl点。在这里，高等人使用了一种专为千兆赫频率设计的切割金属丝准晶体。观察光子节线简并以及由此产生的光子Weyl点。
Nodal line semimetals (NLS) are three-dimensional (3D) crystals that support band crossings in the form of one-dimensional rings in the Brillouin zone. In the presence of spin–orbit coupling or lowered crystal symmetry, NLS may transform into Dirac semimetals, Weyl semimetals, or 3D topological insulators. In the photonics context, despite the realization of topological phases, such as Chern insulators, topological insulators, Weyl, and Dirac degeneracies, no experimental demonstration of photonic nodal lines (NLs) has been reported so far. Here, we experimentally demonstrate NL degeneracies in microwave cut-wire metacrystals with engineered negative bulk plasma dispersion. Both the bulk and surface states of the NL metamaterial are observed through spatial Fourier transformations of the scanned near-field distributions. Furthermore, we theoretically show that the NL degeneracy can transform into two Weyl points when gyroelectric materials are incorporated into the metacrystal design. Our findings may inspire further advances in topological photonics. Nodal lines are 1D band crossings forming a ring in the Brillouin zone which can spawn Weyl points. Here, using a cut-wire metacrystal designed for gigahertz frequencies, Gao et al. observe photonic nodal line degeneracies as well as the photonic Weyl points arising from them.
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通讯作者：
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