Higher-order Dirac semimetal in a photonic crystal

• Main Authors: Wang, Zihao, Liu, Dongjue, Teo, Hau Tian, Wang, Qiang, Xue, Haoran, Zhang, Baile
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2022
• Subjects: Science::Physics::Optics and light; Photonic Crystals; Topological Insulators
• Online Access: https://hdl.handle.net/10356/156871
• Institution: Nanyang Technological University

The recent discovery of higher-order topology has largely enriched the classification of topological materials. Theoretical and experimental studies have unveiled various higher-order topological insulators that exhibit topologically protected corner or hinge states. More recently, higher-order topology has been introduced to topological semimetals. Thus far, realistic models and experimental verifications on higher-order topological semimetals are still very limited. Here we design and demonstrate a three-dimensional photonic crystal that realizes a higher-order Dirac semimetal phase. Numerical results on the band structure show that the designed three-dimensional photonic crystal is able to host two fourfold Dirac points, which are connected in the momentum-space projections via higher-order hinge states localized at the hinge. The higher-order topology can be characterized by the topological invariant χ(6) at different values of k_z . An experiment at microwave frequencies is also presented to measure the hinge state dispersion. Our work demonstrates the physical realization of a higher-order Dirac semimetal phase and paves the way to explore higher-order topological semimetal phases in three-dimensional photonic systems.