Solitonlike Propagation of Zero Sound in SuperfluidHe3

Abstract

We report observations of nonlinear phenomena in the propagation of zero-sound pulses near a collective-mode attenuation peak in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$. These include saturation of the sound absorption, amplitude dependence of the group velocity, and pulse breakup. Our data show effects similar to those observed in nonlinear optical systems. We suggest that above a threshold input level, the sound pulse propagates as a soliton.