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

Abstract

It is of fundamental interest to probe dynamics excitations such as magnons with nanoscale wavelengths in matter. Here, the authors experimentally observe magnons with high k-vectors using Brillouin light scattering microscopy with the use of dielectric nanoresonators, which opens the way for the future nanoscale magnonics research and probing materials with high-momentum photons. Local probing of dynamic excitations such as magnons and phonons in materials and nanostructures can bring new insights into their properties and functionalities. For example, in magnonics, many concepts and devices recently demonstrated at the macro- and microscale now need to be realized at the nanoscale. Brillouin light scattering (BLS) spectroscopy and microscopy has become a standard technique for spin wave characterization, and enabled many pioneering magnonic experiments. However, the conventional BLS cannot detect nanoscale waves due to its fundamental limit in maximum detectable quasiparticle momentum. Here we show that optically induced Mie resonances in nanoparticles can be used to extend the range of accessible quasiparticle's wavevectors beyond the BLS fundamental limit. These experiments involve the measurement of thermally excited as well as coherently excited high momentum magnons. Our findings demonstrate the capability of Mie-enhanced BLS and significantly extend the usability of BLS microscopy for magnonic and phononic research.It is of fundamental interest to probe dynamics excitations such as magnons with nanoscale wavelengths in matter. Here, the authors experimentally observe magnons with high k-vectors using Brillouin light scattering microscopy with the use of dielectric nanoresonators, which opens the way for the future nanoscale magnonics research and probing materials with high-momentum photons. Local probing of dynamic excitations such as magnons and phonons in materials and nanostructures can bring new insights into their properties and functionalities. For example, in magnonics, many concepts and devices recently demonstrated at the macro- and microscale now need to be realized at the nanoscale. Brillouin light scattering (BLS) spectroscopy and microscopy has become a standard technique for spin wave characterization, and enabled many pioneering magnonic experiments. However, the conventional BLS cannot detect nanoscale waves due to its fundamental limit in maximum detectable quasiparticle momentum. Here we show that optically induced Mie resonances in nanoparticles can be used to extend the range of accessible quasiparticle's wavevectors beyond the BLS fundamental limit. These experiments involve the measurement of thermally excited as well as coherently excited high momentum magnons. Our findings demonstrate the capability of Mie-enhanced BLS and significantly extend the usability of BLS microscopy for magnonic and phononic research.