Chiral photonic topological states in Penrose quasicrystals

Electromagnetic topological edge states typically are cre-ated in photonic systems with crystalline symmetry and these states emerge because of the topological feature of bulk Bloch bands in momentum space according to the bulk-edge cor-respondence principle. In this work, we demonstrate the existence of chiral topological electromagnetic edge states in Penrose-tiled photonic quasicrystals made of magneto -optical materials, without relying on the concept of bulk Bloch bands in momentum space. Despite the absence of bulk Bloch bands, which naturally defiles the conventional definition of topological invariants in momentum space char-acterizing these states, such as the Chern number, we show that some bandgaps in these photonic quasicrystals still could host unidirectional topological electromagnetic edge states immune to backscattering in both cylinders-in-air and holes-in-slab configurations. Employing a real-space topo-logical invariant based on the Bott index, our calculations reveal that the bandgaps hosting these chiral topological edge states possess a nontrivial Bott index of +/- 1, depending on the direction of the external magnetic field. Our work opens the door to the study of topological states in photonic quasicrystals. (c) 2023 Optica Publishing Group

Automated summary

In this work, the existence of chiral topological electromagnetic edge states in Penrose-tiled photonic quasicrystals made of magneto-optical materials is demonstrated, without relying on the concept of bulk Bloch bands in momentum space. Despite the absence of bulk Bloch bands, some bandgaps in these photonic quasicrystals still could host unidirectional topological electromagnetic edge states immune to backscattering. Employing a real-space topological invariant based on the Bott index, it is shown that the bandgaps hosting these chiral topological edge states possess a nontrivial Bott index, depending on the direction of the external magnetic field. This work opens new possibilities for the study of topological states in photonic quasicrystals.