Study The Topological Properties Of Photonic Semimetal

Topological physics is a hot topic for more than a decade.Depending on whether there is a complete gap between conduction bands and valence bands,the topological phase can be categorized into two classes:gapped and gapless.In this paper,we mainly focus on the gapless photonic topological semimetals,such as the photonic Dirac semimetal,photonic Weyl semimetal and photonic nodal line semimetal,and the related physical properties.The contents are listed as follows:1.Stretchable photonic‘Fermi arcs’in twisted magnetized plasma.As the cyclotron resonance frequency exceeds the plasma frequency,there exsit a pair of Weyl points with opposite chirality in the momentum space of magnetized plasma.The connection properties of the‘Feimi arcs’are analyzed based on effective Weyl Hamiltonian.By changing the relative magnitude and relative orientation of the applied DC magnetic field between the two magnetized plasmas,the photonic‘Fermi Arcs’can be arbitaryly stretched.The fast numerical method based on 4×4 matrix for calculating the surface states between two materials interface is proposed.2.Experimental observation of photonic hourglass nodal line.By introducing glide symmetry into meta-crystal,the hourglass nodal line dispersion bands are realized.The formation mechanism of the hourglass line nodal dispersion is well explained from the perspective of space symmetry.Also,for the first time,the photonic hourglass shaped line nodal dispersion is observed in the meta-crystal at microwave region.3.Realizing photonic exceptional point in Kerr nonlinear system.Two symmetric Kerr nonlinear optical resonators will exhibit spontaneous symmetry breaking with the increase of light pump,which tune two mirror symmetry modes into asymmetric.In the case of an asymmetric distribution,the exceptional point appears at certain input light intensity.In addition,by arranging the Kerr nonlinear optical resonantor into honeycomb structure,the exceptional point exist in the K and K′points in the Brillouin zone and exhibit nontrivial Berry curvature properties.