• Photonics Research
  • Vol. 9, Issue 9, 09001854 (2021)
Hai-Xiao Wang1、4、†、*, Li Liang1、†, Bin Jiang2, Junhui Hu1, Xiancong Lu3, and Jian-Hua Jiang2、5、*
Author Affiliations
  • 1School of Physical Science and Technology, Guangxi Normal University, Guilin 541004, China
  • 2School of Physical Science and Technology, Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006, China
  • 3Department of Physics, Xiamen University, Xiamen 361005, China
  • 4e-mail: hxwang@gxnu.edu.cn
  • 5e-mail: jianhuajiang@suda.edu.cn
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    We demonstrate that multiple higher-order topological transitions can be triggered via the continuous change of the geometry in kagome photonic crystals composed of three dielectric rods. By tuning a single geometry parameter, the photonic corner and edge states emerge or disappear with higher-order topological transitions. Two distinct higher-order topological insulator phases and a normal insulator phase are revealed. Their topological indices are obtained from symmetry representations. A photonic analog of the fractional corner charge is introduced to distinguish the two higher-order topological insulator phases. Our predictions can be readily realized and verified in configurable dielectric photonic crystals.


    Topological phases and phase transitions have been extensively studied in electronic [1,2], photonic [3], and acoustic [4,5] systems in the past decades. Recently, a new class of topological insulators, called higher-order topological insulators (HOTIs) that are characterized by higher-order bulk-boundary (e.g., bulk-corner or bulk-hinge) correspondence, were discovered [636]. HOTIs set up examples with multidimensional topological physics going beyond the bulk-edge correspondence in conventional topological insulators and semimetals and thus attract growing attention. Prototype HOTIs include quadrupole and octupole topological insulators [616,37,38], 3D HOTIs in electronic systems with topological hinge states [1720], and HOTIs with quantized Wannier centers [2134,3941]. Among these prototype HOTIs, the breathing kagome lattice is regarded as an excellent platform to study higher-order topological phases and phase transitions. It was first proposed in Ref. [21], and subsequently experimentally realized in acoustic [22,23] and photonic [24,25] systems. In the breathing kagome lattice, the higher-order topology is characterized by the quantized bulk polarization (or the position of the Wannier center). When there is a mismatch between the Wannier center and the lattice site, the breathing kagome lattice becomes a higher-order topological phase and exhibits gapped edge states and in-gap corner states. On the contrary, the breathing kagome lattice becomes a topological trivial phase when the Wannier center overlaps with the lattice site. Despite extensive studies on HOTIs based on the breathing kagome lattice, most studies only distinguish the higher-order topological phases from the trivial phases. As a result, the distinctions between two higher-order topological phases and phase transitions have not yet been revealed.

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    Hai-Xiao Wang, Li Liang, Bin Jiang, Junhui Hu, Xiancong Lu, Jian-Hua Jiang. Higher-order topological phases in tunable C3 symmetric photonic crystals[J]. Photonics Research, 2021, 9(9): 09001854
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    Category: Optical and Photonic Materials
    Received: Jun. 4, 2021
    Accepted: Jul. 20, 2021
    Published Online: Sep. 1, 2021
    The Author Email: Hai-Xiao Wang (hxwang@gxnu.edu.cn), Jian-Hua Jiang (jianhuajiang@suda.edu.cn)