An Exact Energy Conservation Law for Magneto-Optical Nanoparticles

TL;DR

This paper derives an exact energy conservation law for magneto-optical nanoparticles, revealing fundamental bounds on their polarizabilities and identifying regimes of allowed and forbidden scattering behaviors.

Contribution

It provides the first exact energy conservation law for axially symmetric magneto-optical nanoparticles under general conditions.

Findings

Purely magneto-optical scattering is fundamentally forbidden.

Strong magneto-optical scattering regimes are allowed.

Energy bounds constrain nanoparticle polarizabilities.

Abstract

Energy conservation imposes fundamental bounds on the polarizabilities of nanoparticles (NPs). While such bounds are well established for isotropic and bianisotropic NPs, they remain unexplored for magneto-optical NPs. Here, we derive the exact energy-conservation law governing the electric and magnetic dipolar response of axially symmetric magneto-optical NPs under general illumination conditions and arbitrary external magnetic fields. Two central results follow from energy conservation: (i) purely magneto-optical scattering, where the non-magnetic polarizability vanishes, is fundamentally forbidden, and (ii) strong magneto-optical scattering regimes, in which the magneto-optical polarizability dominates, are intriguingly allowed.