Abstract
We demonstrate that topologically nontrivial states of light can be engineered in periodic photonic structures containing media with a Tellegen-type bianisotropic response. Whilst in such bianisotropic materials the time-reversal symmetry is broken, they are characterized by an intrinsic magnetic order which does not require macroscopic magnetization. Our design can therefore be considered as a direct analog of the solid state Chern insulator which exhibits a topological order in the absence of an external bias. Numerical simulations of such Tellegen photonic crystals reveal the existence of one-way edge transport at domain walls and perfectly conducting boundaries not sensitive to structural imperfections such as local defects and disorder. We demonstrate a scheme for achieving robust steering of the edge modes by controlling the phase and amplitude of the source.
Highlights
The past three decades have witnessed the discovery of condensed matter systems characterized by topological order, in particular topological insulators [1,2,3,4]—a development which has significantly enriched our understanding of wave phenomena in numerous branches of physics [5,6,7,8,9,10]
The introduction of gain and loss, as well as some forms of bianisotropic response allow the removal of TR symmetry and it is natural to investigate these in the context of realizing topological order for light
In addition to domain walls where the Tellegen parameter χ switches sign we have found that one-way edge modes appear at terminations of the Tellegen photonic crystals (TPC) by a perfect electric conductor (PEC) (figure 2(b), field profiles not shown)
Summary
The past three decades have witnessed the discovery of condensed matter systems characterized by topological order, in particular topological insulators [1,2,3,4]—a development which has significantly enriched our understanding of wave phenomena in numerous branches of physics [5,6,7,8,9,10]. One of the main advantages of considering TR broken systems stems from the fact that the resulting topological protection is extremely robust [7, 14, 26] This is in sharp contrast to the alternative approach based on realizing symmetry protected topological phases (photonic analogs of the quantum spin Hall effect), including that found in bianisotropic meta-crystals, where topological properties exist only to the extent that ˆ = mor similar constraints can be engineered [19, 24], a constraint which ensures pseudo-spin conservation in the structure.
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