Direct Observation of Flatband Loop States Arising from Nontrivial Real-Space Topology
Direct Observation of Flatband Loop States Arising from Nontrivial Real-Space Topology
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直接观察非平凡实空间拓扑产生的平带环路状态
DOI：
10.1103/physrevlett.124.183901
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发表时间：
2020-05-04
影响因子：
8.6
通讯作者：
Chen, Zhigang
中科院分区：
文献类型：
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作者：
Ma, Jina;Rhim, Jun-Won;Chen, Zhigang
格的拓扑性质通常在动量空间中使用陈数等概念来揭示。在这里，我们研究非常规的回路状态，即不可收缩回路状态（NLS）和鲁棒边界模式，介导的非平凡拓扑在真实的空间。虽然这种状态在理解平带系统的基础物理学方面发挥着关键作用，但由于实现所需边界条件的挑战，它们的实验观察受到了阻碍。使用激光写入技术，我们光学地建立光子kagome晶格与开放的边界通过适当截断晶格，和周期性的边界通过塑造晶格成一个科尔宾几何形状。因此，我们证明了强大的边界模式周围的开放晶格的整个边缘缠绕，更直接地，NLS缠绕在一个闭环类似于在一个环面。我们证明了由于实空间拓扑的NLS坚持在理想的Corbino形kagome格的任意大小。我们的结果对于理解奇异平带和强相互作用系统中有趣的物理现象具有重要意义。
Topological properties of lattices are typically revealed in momentum space using concepts such as the Chern number. Here, we study unconventional loop states, namely, the noncontractible loop states (NLSs) and robust boundary modes, mediated by nontrivial topology in real space. While such states play a key role in understanding fundamental physics of flatband systems, their experimental observation has been hampered because of the challenge in realizing desired boundary conditions. Using a laser-writing technique, we optically establish photonic kagome lattices with both an open boundary by properly truncating the lattice, and a periodic boundary by shaping the lattice into a Corbin geometry. We thereby demonstrate the robust boundary modes winding around the entire edge of the open lattice and, more directly, the NLSs winding in a closed loop akin to that in a torus. We prove that the NLSs due to real-space topology persist in ideal Corbino-shaped kagome lattices of arbitrary size. Our results could be of great importance for our understanding of the singular flatbands and the intriguing physics phenomenon applicable for strongly interacting systems.