A Universal Magnetoelectric Limit for Chiral and Tellegen Bi-Isotropic Scatterers

TL;DR

This paper establishes a universal energy-based upper limit on the magnetoelectric coupling of bi-isotropic nanoparticles, applicable to both chiral and Tellegen types, regardless of material or illumination specifics.

Contribution

It introduces a universal bound on magnetoelectric coupling for bi-isotropic nanoparticles, independent of material properties and reciprocity, applicable across all scattering channels.

Findings

Derived a universal energy conservation-based bound on magnetoelectric coupling.

Showed the bound applies to both chiral and Tellegen nanoparticles.

Demonstrated the bound's applicability across all multipolar scattering channels.

Abstract

We reveal the existence of a universal upper bound on the magnetoelectric coupling of any bi-isotropic nanoparticle. The bound arises solely from energy conservation, making it independent of the specific material properties of the nanoparticle and illumination conditions. Moreover, the bound does not rely on reciprocity, being identical for reciprocal (chiral) and non-reciprocal (Tellegen) nanoparticles. We further show that the chiral Mie coefficient of spherical particles of arbitrary optical size obeys the same bound across all multipolar scattering channels. Our results introduce a universal metric on the magnetoelectric coupling of bi-isotropic objects, setting identical limits on chiral and Tellegen light-matter interactions at the single particle level.