Differential chiral sensing at exceptional points in intrinsically chiral metastructures

Abstract

Discriminating opposite enantiomers through their weak chiroptical responses remains a fundamental challenge in optical sensing. Exceptional points (EPs), non-Hermitian singularities at which eigenvalues and eigenvectors coalesce, offer a route to enhanced spectral responses through their characteristic square-root eigenvalue splitting. However, their potential for chiral discrimination remains largely unexplored. We demonstrate exceptional points in an intrinsically chiral hybrid metamaterial and reveal strongly asymmetric responses to enantiomeric perturbations. The interplay between intrinsic chirality and non-Hermitian degeneracy is realized through the coupling of a chiral plasmonic nanoantenna array to a photonic crystal slab. We observe characteristic complex-square-root scaling, with both resonance frequencies and loss-rates exhibiting pronounced handedness dependence. Remarkably, opposite enantiomers produce complex mode splittings that differ by more than an order of magnitude. Our findings establish intrinsic chirality as a new degree of freedom in non-Hermitian physics and reveal a fundamental route toward topological singularities enhanced discrimination of chiral matter.