Mie-enhanced microfocused Brillouin light scattering for full wave vector resolution of nanoscale spin waves.

Abstract

Magnons, the quanta of spin waves, are magnetic excitations of matter spanning through the entire crystal's Brillouin zone and covering a wide range of frequencies ranging from subgigahertz to terahertz. Magnons play a crucial role in many phenomena, such as the reduction of saturation magnetization with increasing temperature or the Bose-Einstein condensation. However, established experimental techniques cannot resolve magnons with wave vectors between 30 and 300 rad μm^-1. We address this gap by tailoring the Brillouin light scattering process with dielectric periodic nanostripes hosting Mie resonances. This approach enables access to the previously unmeasurable wave vector range while providing at the same time full wave vector resolution, all within a tabletop setup. Filling this gap can stimulate further experimental investigations of the fundamental phenomena associated with magnons as well as applications in computational and microwave devices. In addition, the same methodology can be applied to other excitations of matter, such as phonons, opening up possibilities in, e.g., mechanobiological studies.