Zero-sound attenuation in rotating and stationary³He-A and³He-B

We report on measurements of zero-sound attenuation in rotating and stationary³He-A and³He-B, in magnetic fields up to 350 mT. Strong and highly nonlinear rotation speed dependencies of sound amplitudes have been observed in both phases. The data gives information on vortex types and core sizes, although the analysis is not straightforward. The anomalous attenuation in³He-B at 200 mT near the AB transition, both in the stationary and in the rotating state, is interpreted to arise from the distortion of the energy gap of the B phase. Excess attenuation during the AB phase change was observed. Evidence for soft vortex cores in³He-B is presented. In addition, a critical velocity in the vortex free state, related to a textural transition, and the vortex creation times have been measured in³He-B. Furthermore, a metastable structure, possibly a new vortex state, has been observed in³He-B by rotating the sample through the A → B transition.