Non-linear Stationary Spin-waves in Superfluid 3He-B at Ultra-low Temperatures

We have performed detailed CW NMR measurements on superfluid³He-B in order to investigate stationary spin-wave modes in a texture well. Our results at high temperatures are consistent with previous work. However, we find that the spin dynamics is profoundly modified, even for small excitation amplitudes, for temperatures on the order of 200 K, substantially lower than the limit reached in previous investigations. We report the observation of non-linear spin-waves at ultra-low temperatures and their characterization in terms of a third-order anharmonic oscillator.