Fourth sound shock waves in 3He-B

The relative density of the superfluid component of 3He is expected to be significantly depressed by flow. For this reason the distortion of a finite amplitude fourth sound wave exhibits an unusual amplitude dependence. For waves of sufficiently large initial amplitude, a fully developed shock wave will contain two discontinuities per wavelength. Waves of amplitude twenty times greater than the threshold for this unusual behavior have been reported in the literature. (orig.)