The Emergence of Topological Nodal Points in Photonic Crystal with Mirror Symmetry

TL;DR

This paper demonstrates that mirror symmetry in photonic crystals can lead to the emergence of topological nodal points, which can be manipulated to realize photonic Chern insulators and helical edge states.

Contribution

It reveals the mechanism of topological nodal point formation in mirror-symmetric photonic crystals and explores their manipulation via symmetry breaking.

Findings

Topological nodal points emerge in mirror-symmetric photonic crystals.

Breaking mirror symmetry unbuckles the nodal points, enabling Chern insulator states.

Breaking time reversal and inversion symmetries enhances edge state engineering.

Abstract

We show that topological nodal points can emerge in photonic crystal possessing mirror symmetry. The mechanism of generating topological nodal points is discussed in a two-dimensional photonic square lattice, in which four topological nodal points split out naturally after the touching of two bands with different parity. The emergence of such nodal points, characterized by vortex structure in momentum space, is attributed to the unavoidable band crossing protected by mirror symmetry. The topological nodes can be unbuckled through breaking the mirror symmetry and a photonic Chern insulator can be achieved through time reversal symmetry breaking. The joint effect of breaking time reversal symmetry and breaking inversion symmetry is further found to strengthen the finite size effect, providing ways to engineer helical edge states.