论文标题
拓扑平带循环状态在类似分形光子晶格中
Topological flatband loop states in fractal-like photonic lattices
论文作者
论文摘要
不合理的循环状态(NLSS)最近是在平板晶格中实现的拓扑实体,通常是由于平坦带相交一个或多个分散频段的点所产生的。也存在跨过一架飞机的乐队接触,其中一条平面带在布里渊区的整个区域中重叠,而无需越过分散频带。这种孤立的平面平坦带仍然没有探索。例如,与这种平面变性相关的拓扑特征是什么?在这里,我们首次证明了我们的知识非平凡的NLS和稳健的边界模式。基于量身定制的光子晶格,该光子晶格由众所周知的分形Sierpinski垫圈构建,我们理论上分析了波功能奇点和存在NLSS的条件。我们表明,NLS可以以奇异和非词形平面波段存在,作为真实空间拓扑的直接反映。在实验上,我们直接观察到激光写入的Corbino形状的晶格中的这种平板NLS。这项工作不仅可以深入了解非平凡的平板状态背后的机制,而且还开辟了新的途径,以探索源自平面退化,分形结构和带拓扑的相互作用引起的基本现象。
Noncontractible loop states (NLSs) are recently realized topological entity in flatband lattices, arising typically from band touching at a point where a flat band intersects one or more dispersive bands. There exists also band touching across a plane, where one flat band overlaps another all over the Brillouin zone without crossing a dispersive band. Such isolated plane-touching flat bands remain largely unexplored. For example, what are the topological features associated with such flatband degeneracy? Here, we demonstrate for the first time to our knowledge nontrivial NLSs and robust boundary modes in a system with such degeneracy. Based on a tailored photonic lattice constructed from the well-known fractal Sierpinski gasket, we theoretically analyze the wavefunction singularities and the conditions for the existence of the NLSs. We show that the NLSs can exist in both singular and nonsingular flat bands, as a direct reflection of the real-space topology. Experimentally, we observe directly such flatband NLSs in a laser-written Corbino-shaped fractal-like lattice. This work not only leads to a deep understanding of the mechanism behind the nontrivial flatband states, but also opens up new avenues to explore fundamental phenomena arising from the interplay of flatband degeneracy, fractal structures and band topology.