Twisted Quadrupole Topological Photonic Crystals

• Published in: Laser & photonics reviews Vol. 14; no. 8
• Main Authors: Zhou, Xiaoxi, Lin, Zhi‐Kang, Lu, Weixin, Lai, Yun, Hou, Bo, Jiang, Jian‐Hua
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.08.2020
• Subjects: Crystal lattices; Heterostructures; higher‐order topology; Metamaterials; Photonic crystals; Polaritons; quadrupole topology; Quadrupoles; Topological insulators; topological photonics; Topology; Twisting
• DOI: 10.1002/lpor.202000010
• ISSN: 1863-8880

Topological manipulation of waves is at the heart of cutting‐edge metamaterial research. Quadrupole topological insulators were recently discovered in 2D flux‐threading lattices that exhibit higher‐order topological wave trapping at both the edges and corners. Photonic crystals (PhCs), lying at the boundary between continuous media and discrete lattices, however, are incompatible with the present quadrupole topological theory. Here, quadrupole topological PhCs triggered by a twisting degree‐of‐freedom are unveiled. Using a topologically trivial PhC as the motherboard, it is shown that twisting induces quadrupole topological PhCs without flux‐threading. The twisting‐induced crystalline symmetry enriches the Wannier polarizations and leads to the anomalous quadrupole topology. Versatile edge and corner phenomena are observed by controlling the twisting angles in a lateral heterostructure of 2D PhCs. This study paves the way toward topological twist photonics as well as the quadrupole topology in the quasi‐continuum regime for phonons and polaritons. Twisting is a novel way for the manipulation of waves in 2D electronic and photonic systems. While Moiré patterns are formed by twisting in bilayers or trilayers, here, it is demonstrated that lateral heterostructures of twisted 2D photonic crystals lead to higher‐order topology and induce corner states. This provides a convenient approach toward higher‐order topological phenomena in dielectric photonic metamaterials.