Observation of Bulk Fermi Arc and Polarization Half Charge from Paired Exceptional Points

TL;DR

This paper reports the discovery and experimental demonstration of a topologically protected bulk Fermi arc and polarization half charge arising from non-Hermitian exceptional points in photonic systems, linking topological photonics and non-Hermitian physics.

Contribution

It introduces a new non-Hermitian topological phenomenon involving bulk Fermi arcs and polarization half charges, expanding the understanding of topological effects beyond Hermitian systems.

Findings

Demonstration of a bulk Fermi arc from non-Hermitian losses

Observation of polarization half-integer topological charges

Connection of phenomena to exceptional points in non-Hermitian physics

Abstract

The ideas of topology have found tremendous success in Hermitian physical systems, but even richer properties exist in the more general non-Hermitian framework. Here, we theoretically propose and experimentally demonstrate a new topologically-protected bulk Fermi arc which---unlike the well-known surface Fermi arcs arising from Weyl points in Hermitian systems---develops from non-Hermitian radiative losses in photonic crystal slabs. Moreover, we discover half-integer topological charges in the polarization of far-field radiation around the Fermi arc. We show that both phenomena are direct consequences of the non-Hermitian topological properties of exceptional points, where resonances coincide in their frequencies and linewidths. Our work connects the fields of topological photonics, non-Hermitian physics and singular optics, and paves the way for future exploration of non-Hermitian topological systems.