Broadband negative refraction based on a pair of anti-parity-time structures

This is the authors' abstract. We don't add key points for this paper.

An anti-parity-time (A-PT) symmetric system, of which the refractive index satisfies , can present intriguing scattering properties like continuous coherent perfect absorption (CPA) spectrum and laser spectrum, which are symmetric to each other in the parameter space. In this work, an acoustic parity-time (PT) symmetric system consisting of two A-PT symmetric structures is introduced to realize a broadband negative refraction. When the two A-PT symmetric structures are at their CPA mode and laser mode, respectively, the PT symmetric system can display its unidirectional negative refraction property. As the two A-PT structures we design here have a broadband CPA and laser modes, the PT symmetric negative refraction system will be broadband. Besides, the exceptional point (EP) of the proposed PT symmetric system corresponds to the CPA point and laser point of its two components, and it is unidirectionally transparent on broadband as well.