EXCEPTIONAL POINTS IN PARITY–TIME-SYMMETRIC SUBWAVELENGTH METAMATERIALS

When sources of energy gain and loss are introduced to a wave scattering system, the underlying mathematical formulation will be non-Hermitian. This paves the way for the existence of exceptional points, where eigenmodes are linearly dependent. The primary goal of this work is to study the existence of exceptional points in high-contrast subwavelength metamaterials. We begin by studying a parity–time-symmetric pair of subwavelength resonators and prove that this system supports asymptotic exceptional points. These are points at which the subwavelength eigenvalues and eigenvectors coincide at leading order in the asymptotic parameter. We then investigate the exotic scattering behavior of a metascreen composed of repeating parity–time-symmetric pairs of subwavelength resonators. We prove that the non-Hermitian nature of this structure means that it exhibits asymptotic unidirectional reflectionless transmission at certain frequencies and demonstrate extraordinary transmission close to these frequencies.