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Public Seminar of PhD Candidate:
Theoretical Studies of PT Symmetric Topological Gapless Photonic Crystals


Speaker:Mr. Biye XIE
Affiliation:The University of Hong Kong
Date:November 24, 2017 (Friday)
Time:9:30 a.m.
Venue:Rm 518, 5/F, Chong Yuet Ming Physics Building, HKU

Abstract
 

Topological gapless materials such as topological semimetals and topologicalmetals have attracted enormous attentions in recent years due to their uniquetopological transport properties and topological protected surface states. Although it is not difficult to realize band degeneraciesin electronicmaterials, to ensure that the Fermi energy is exactly at the level which the degenerate points located at is not easy. This is the main obstacle to realizetheoretically predicted topological gapless models in electronic materials.

In this study, we focus on the photonic crystals (PhCs) which are periodically arrayed dielectric materials. The diverse band structures and symmetry properties in PhCs provide people with platforms to study the topological gapless and gapped band structures. Here we consider a new type of PhCs with the combination of time reversal (T) symmetry and parity (P) symmetry, the PT symmetry. We find that, in our PhC, even if the T symmetry and the P symmetry are both broken, the PhC has gapless points which are protect by the existing PT symmetryat the Brillouin zone corners. We provide the derivation of the effective Hamiltonian near the gapless points based on the irreducible representation group theory as well as thenumerical calculation of the band structures. We point out that these gapless points are characterized by a Z2 topological charge. Furthermore we find that these topological protected gapless points in PhC belong to different topological class compared to the gapless PhCs with both T symmetry and P symmetry in previous studies.

Anyone interested is welcome to attend.