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

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 φ becomes elliptically polarized. The polarization azimuth rotation and ellipticity angle variation are sinusoidal functions of 2φ. 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 2φ. Near the surface plasmon frequency, Faraday rotation and Faraday ellipticity increase.