Faraday rotation and circular dichroism spectra of gold and silver nanoparticle aggregates

Abstract

We study the magneto-optical response of noble metal nanoparticle clusters. We consider the interaction between the light-induced dipoles of particles. In the presence of a magnetic field, the simplest achiral cluster, a dimer, exhibits circular dichroism (CD). The CD of a dimer depends on the directions of the magnetic field and the light wave vector. The CD of a populous cluster weakly depends on the magnetic field. Upon scattering from the cluster, an incident linearly polarized light with polarization azimuth $\ensuremath{\varphi}$ becomes elliptically polarized. The polarization azimuth rotation and ellipticity angle variation are sinusoidal functions of $2\ensuremath{\varphi}$. The anisotropy and the chirality of the cluster control the amplitude and offset of these sinusoidal functions. The Faraday rotation and Faraday ellipticity are also sinusoidal functions of $2\ensuremath{\varphi}$. Near the surface plasmon frequency, Faraday rotation and Faraday ellipticity increase.