Spatially extended nonlinear generation of short-wavelength spin waves in yttrium iron garnet nanowaveguides

We experimentally study the nonlinear propagation of spin waves in nanoscale yttrium iron garnet waveguides, where the dispersion spectrum is engineered to enable efficient four-magnon interactions over a wide range of wavelengths. We show that, under these conditions, the initial monochromatic spin wave nonlinearly generates copropagating spin waves with well-defined, discrete frequencies. This process is characterized by a low energy threshold and can be observed in a wide range of frequencies and excitation powers. Thanks to the engineered dispersion, the process enables the generation of waves with short wavelengths that cannot be excited directly by a linear excitation mechanism. The nonlinearly generated short-wavelength spin waves continuously acquire the energy from the initial pump wave during copropagation, which results in compensation for their propagation losses over significant distances. The observed phenomena can be used to implement frequency- and wavelength-conversion operations in magnonic nanodevices and circuits.