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, highfrequency 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.

Phonon transport in the gigahertz to terahertz range: Confinement, topology, and second sound

“…We discuss how the recently developed pumped BLS approach can be used to study acoustic Anderson localization, one-way transport in acoustic diodes, and topological acoustics. In the discussion of BLS we omit its use on the biomedical sector [28][29][30][31] and on spintronics (magnonics) [32][33][34][35] . Finally, we turn our attention to thermal waves, otherwise known as Second Sound.…”

Phase-resolved optical characterization of nanoscale spin waves

“…The above equation highlights the importance of field localization provided by the silicon disks: the spatial profile of E determines the area that contributes to the collected BLS signal. If the modulation of the spatial profile of E is larger than the spin-wave wavelength, the exponential factor e ikm•r is averaged out and the information about the spin wave is lost [20,32]. On the other hand, intense hotspots generated by the silicon disk effectively limit the spatial extent of the induced polarization to a very small volume and thus facilitate the extraction of the spin-wave phase from BLS measurements.…”

Observing high-k magnons with Mie-resonance-enhanced Brillouin light scattering

“…For the laser wavelength λ i = 532 nm, for example, the maximum k-vector that can be theoretically detected is k max mag ¼ 23:6 rad μm −1 , which corresponds to a minimum spin-wave wavelength λ min mag ¼ λ i =2 ¼ 266 nm 1,2 . Taking an inspiration from tip-and surface-enhanced Raman scattering spectroscopy [11][12][13] , nanosized apertures or other plasmonic structures made of metals have been used to locally enhance the electromagnetic field and increase the range of the accessible k-vectors [14][15][16] . Unfortunately, the efficiency of the plasmonic approach is severely limited by high optical losses in metallic structures which makes it unsuitable for convenient magnon measurements (see 16 and Supplementary Fig.…”