Ultrasonic investigation of rotating³He-B in strong magnetic fields

We have studied ultrasonic attenuation in rotating ³He-B at low pressures (< 10 bar) in magnetic fields up to 300 mT. In a strong field, the energy gap Δ in ³He-B is anisotropic, and the attenuation α of zero sound depends on the orientation of Δ. Because vortices and the counterflow between the normal and superfluid components of the liquid turn the anisotropy axis of Δ, a clear dependence of α on the rotation velocity Ω can be observed. The magnitude of this response is not a linear, sometimes not even a monotonic function of Ω. Its dependence on the magnetic field is anomalous around H = 200 mT. We have also observed a metastable state in rotating ^3He-B, which can be created by rotating the sample while cooling through the AB-transition. The lifetime of this state is on the order of 10 minutes.