Tesla-Range Femtosecond Pulses of Stationary Magnetic Field, Optically Generated at the Nanoscale in a Plasmonic Antenna

The inverse Faraday effect allows the generation of stationary magnetic fields through optical excitation only. This light-matter interaction in metals results from creating drift currents via nonlinear forces that light applies to the conduction electrons. Here, we describe the theory underlying the generation of drift currents in metals, particularly its application to photonic nanostructures using numerical simulations. We demonstrate that a gold photonic nanoantenna, optimized by a genetic algorithm, allows, under high excitation power, to maximize the drift currents and generate a pulse of stationary magnetic fields in the tesla range. This intense magnetic field, confined at the nanoscale and for a few femtoseconds, results from annular optical confinement and not from the creation of a single optical hot spot. Moreover, by controlling the incident polarization state, we demonstrate the orientation control of the created magnetic field and its reversal on demand. Finally, the stationary magnetic field's temporal behavior and the drift currents associated with it reveal the subcycle nature of this light-matter interaction. The manipulation of drift currents by a plasmonic nanostructure for the generation of stationary magnetic field pulses finds applications in the ultrafast control of magnetic domains with applications not only in data storage technologies but also in research fields such as magnetic trapping, magnetic skyrmion, magnetic circular dichroism, to spin control, spin precession, spin currents, and spin-waves, among others.