Magneto-plasmonics is a designation generally associated with ferromagnetic-plasmonic materials because such optical responses from nonmagnetic materials alone are considered weak. Here, we show that there exists a switching transition between linear and nonlinear magneto-optical behaviors in noble-metal nanocolloids that is observable at ultralow illumination intensities and direct current magnetic fields. The response is attributed to polarization-dependent nonzero-time-averaged plasmonic loops, vortex power flows, and nanoparticle magnetization. This work identifies significant mechanical effects that subsequently exist via magnetic-dipole interactions.

We experimentally, analytically, and numerically demonstrate the nonlinear photo-induced plasmon-assisted magnetic response that occurs with metallic nanoparticles in aqueous solution. We measure the scattered spectra from solutions of gold nanospheres (10(-7) fill factor) and observe appreciable changes when simultaneously applying DC magnetic fields and illuminating samples with light. The magnetic response is achieved using light from a solar simulator at unprecedented low illumination intensities (< 1W/cm(2)) and is sustained when the magnetic field is removed. Distinctly different behavior is observed depending on the circular-polarization handedness given a fixed magnetic field. Nanoparticle aggregation is more likely to occur when the circular-polarization trajectory opposes the solenoid current that produces the magnetic field. Using Mie's theoretical solution, we show how vortex orbital surface currents lead to an increased and anisotropic electrical conductivity, which shifts the scattered spectra in agreement with experimental results. The single-nanoparticle plasmon-induced magnetization, which couples the scattered and incident electric fields, changes sign with orthogonal circular-polarization handedness.

There is wide interest in understanding and leveraging the nonlinear plasmon-induced potentials of nanostructured materials. We investigate the electrical response produced by spin-polarized light across a large-area bottom-up assembled 2D plasmonic crystal. Numerical approximations of the Lorentz forces provide quantitative agreement with our experimentally-measured DC voltages. We show that the underlying mechanism of the spin-polarized voltages is a gradient force that arises from asymmetric, time-averaged hotspots, whose locations shift with the chirality of light. Finally, we formalize the role of spin-orbit interactions in the shifted intensity patterns and significantly advance our understanding of the physical phenomena, often related to the spin Hall effect of light.

When plane waves diffract through fractal-patterned apertures, the resulting far-field profiles or diffractals also exhibit iterated, self-similar features. Here we show that this specific architecture enables robust signal transmission and spatial multiplexing: arbitrary parts of a diffractal contain sufficient information to recreate the entire original sparse signal.