Topological Transition Enabled by Surface Modification of Photonic Crystals

Yanxin Lu, Qishan Liu, Yihang Chen*, Zefeng Chen*, Dan-Wei Zhang, Hanying Deng, Shi-Liang Zhu, Peng Han, Nian-Hai Shen, Thomas Koschny, and Costas M. Soukoulis*

Cite this: ACS Photonics 2021, 8, 5, 1385–1392

Publication Date:April 21, 2021

https://doi.org/10.1021/acsphotonics.1c00017

Abstract

Effective mass in the Dirac equation model is generally applied to condensed-matter systems for describing the state of electrons and determining the topological character. In these systems, the sign change of the effective mass is accompanied by a topological transition. Here we demonstrate that the band-gap topological property of a photonic crystal can also be related to a pseudo effective mass that is constructed by mapping Maxwell’s equations to a Dirac-like equation. Then, we propose an efficient method to achieve a sign change of the pseudo effective mass by surface modification, resulting in a topological transition of the photonic crystal. Such a topological transition is confirmed by the emergence of a zero-dimensional topological bound state. We experimentally verify the theoretical predictions via colloidal photonic crystals, where a thin surface coating can lead to the topological transition. Our research provides a new avenue for the manipulation of topological properties of optical systems.