Abstract

We investigate the scattering properties of coupled parity-time (PT) symmetric chiral nanospheres with scattering matrix formalism. The exceptional points, i.e.,spectral singularities at which the eigenvalues and eigenvectors simultaneously coalesce in the parameter space, of scattering matrix can be tailored by the chirality of the nanospheres. We also calculate the scattering, absorption and extinction cross sections of the PT-symmetric chiral scatter under illumination by monochromatic left- and right-circularly polarized plane waves. We find that the scattering cross section of the nanostructures exhibits an asymmetry when the plane waves are incident from the loss and gain regions, respectively, especially in the broken phase, and the optical cross section exhibits circular dichroism, i.e.,differential extinction when the PT-symmetric scatter is endowed with chirality. In particular, under illumination by linearly polarized monochromatic plane waves without intrinsic chirality, the ellipticity of scattered fields in the forward direction, denoting the chirality of light, becomes larger when the scatter is in the PT-symmetry-broken phase. Our findings demonstrate that the gain and loss can control the optical chirality and enhance the chiroptical interactions and pave the way for studying the resonant chiral light-matter interactions in non-Hermitian photonics.

Highlights

  • Chirality, which refers to a geometric handedness of a chiral object that the mirror image cannot be superposed onto itself, is ubiquitous in nature, known for chiral molecules and the double-helix structure of DNA [1]

  • The exceptional points, i.e., spectral singularities at which the eigenvalues and eigenvectors simultaneously coalesce in the parameter space, of scattering matrix can be tailored by the chirality of the nanospheres

  • We find that the scattering cross section of the nanostructures exhibits an asymmetry when the plane waves are incident from the loss and gain regions, respectively, especially in the broken phase, and the optical cross section exhibits circular dichroism, i.e., differential extinction when the PT-symmetric scatter is endowed with chirality

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Summary

Introduction

Chirality, which refers to a geometric handedness of a chiral object that the mirror image cannot be superposed onto itself, is ubiquitous in nature, known for chiral molecules and the double-helix structure of DNA [1]. Various nanostructures and relevant physical mechanisms have been designed and studied to enhance the chiroptical response, including the use of chiral plasmonic nanostructures [5], high-index dielectric nanostructures [6, 7], helicity-preserving optical cavities [8], planar dielectric nanostructures [9] and chiral metamaterials designed by deep learning [10]. We study the light scattering properties of a PT-symmetric chiral nanosphere dimer using the electromagnetic transition matrix (T-matrix) and scattering matrix (S-matrix) [18, 24]. By investigating the influence of chirality and nonHermiticity on the extinction, scattering, absorption cross sections and ellipticity of scattered light of the dimer system, we reveal that the gain and loss play an important role in chiral optical systems that can enhance the chiroptical responses and allow to manipulate exceptional points by the chirality. The interplay between PT-symmetry and chirality investigated in nanoparticle systems can be potentially revealed through far-field scatterings

Methods
T-matrix and S-matrix
Optical cross section
Conclusions

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