Brillouin light scattering of spin waves inaccessible with free-space light

Abstract

Microfocus Brillouin light scattering is a powerful technique for the spectroscopic and spatial characterization of elementary excitations in materials. However, the small momentum of light limits the accessible excitations to the center of the Brillouin zone. Here we utilize a metallic nanoantenna fabricated on the archetypal ferrimagnet yttrium iron garnet to demonstrate the possibility of Brillouin light scattering from large-wave-vector, high-frequency spin wave excitations that are inaccessible with free-space light. The antenna facilitates subdiffraction confinement of the electromagnetic field, which enhances the local field intensity and generates momentum components significantly larger than those of free-space light. Our approach provides access to high-frequency spin waves important for fast nanomagnetic devices, and can be generalized to other types of excitations and light-scattering techniques.