Magnetic field dependence of ultrasound attenuation and sound velocity in superfluid3He-A

Abstract

In the presence of a magnetic field the gap amplitude of the axial state is found to split atall temperatures if particle-hole asymmetry is taken into account. The relative gap splitting is of the order of the relative splitting of the transition temperature and leads to splittings of the frequencies of the clapping and flapping modes. The ultrasonic attenuation and sound velocity are calculated for different sound frequencies, fields, and orientations of the wave vectorq with respect to the axisl of the energy gap. The predicted splittings of the clapping and flapping mode peaks and of the cusp in the attenuation and of the step in the sound velocity atħω=2Δ0(T) should become observable at sufficiently high fields. The results are discussed in connection with ultrasonic impedance, attenuation, and velocity measurements in the A2 and A1 phases.