Ultrasensitive Higher-Order Exceptional Points via Non-Hermitian Zero-Index Materials
Phys. Rev. Lett. 134, 243802 – Published 17 June, 2025
DOI: https://doi.org/10.1103/18gg-gvzc
Abstract
Higher-order exceptional points (EPs) in optical structures enable ultrasensitive responses to perturbations. However, previous investigations on higher-order EPs have predominantly focused on coupled systems, leaving their fundamental physics in open scattering systems largely unexplored. Here, we harness wave interference to realize higher-order EPs in non-Hermitian zero-index materials connected to multiple open channels. Specifically, we show that a three-channel model can give rise to three interesting types of third-order EPs: lasing EP, reflecting EP, and absorbing EP. Notably, near the third-order absorbing EP, we show ultrasensitivity—a drastic change in output power in response to perturbations at the operating frequency—in a purely lossy system. These findings pave the way for achieving higher-order and even arbitrary-order EPs in open scattering systems, offering significant potential for advanced sensing applications.
