Spatially-extended nonlinear generation of short-wavelength spin waves in YIG nanowaveguides

We experimentally study nonlinear propagation of spin waves in microscopic 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 co-propagating 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 allows 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 co-propagation, which results in compensation of their propagation losses over significant distances. The observed phenomena can be used to implement frequency- and wavelength-conversion operations in magnonic nanodevices and circuits.