Realization of robust boundary modes and non-contractible loop states in photonic Kagome lattices

• Published in: arXiv.org 2019-11
• Main Authors: Ma, Jina, Jun-Won Rhim, Tang, Liqin, Xia, Shiqi, Wang, Haiping, Zheng, Xiuyan, Xia, Shiqiang, Song, Daohong, Hu, Yi, Li, Yigang, Bohm-Jung, Yang, Leykam, Daniel, Chen, Zhigang
• Format: Article
• Language: English
• Subjects: Circuits; Continuous wave lasers; Edge effect; Geometry; Graphene; Heterostructures; Kagome lattice; Lattice vibration; Photonics; Quantum electrodynamics; Topology; Toruses; Waveguides
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1911.00848

Corbino-geometry has well-known applications in physics, as in the design of graphene heterostructures for detecting fractional quantum Hall states or superconducting waveguides for illustrating circuit quantum electrodynamics. Here, we propose and demonstrate a photonic Kagome lattice in the Corbino-geometry that leads to direct observation of non-contractible loop states protected by real-space topology. Such states represent the "missing" flat-band eigenmodes, manifested as one-dimensional loops winding around a torus, or lines infinitely extending to the entire flat-band lattice. In finite (truncated) Kagome lattices, however, line states cannot preserve as they are no longer the eigenmodes, in sharp contrast to the case of Lieb lattices. Using a continuous-wave laser writing technique, we experimentally establish finite Kagome lattices with desired cutting edges, as well as in the Corbino-geometry to eliminate edge effects. We thereby observe, for the first time to our knowledge, the robust boundary modes exhibiting self-healing properties, and the localized modes along toroidal direction as a direct manifestation of the non-contractible loop states.