Sound Propagation in Normal and Superfluid 3He
We present measurements of the pressure dependence of the attenuation and velocity of sound in the hydrodynamic regime and in both the normal and superfluid zero sound regime of 3He. The velocity and attenuation were studied at a frequency of 20.24 MHz and at pressures of 17.00, 21.00, 21.50, 21.80, 22.00, 23.17, 26.00, and 28.00 bar in the zero sound regime. In the hydrodynamic region the temperature dependence of the attenuation was studied at 5.48 and 10.02 MHz and at pressures of 0.69, 1.38, and 2.76 bar. At a pressure of 29.3 bar and frequency of 20.24 MHz the transition from hydrodynamic to zero sound behavior was studied for both the velocity and attenuation. In addition, the anisotropy of the velocity and the attenuation as a function of the angle between the direction of an applied external magnetic field and the sound propagation direction was observed in the superfluid A phase at a pressure of 26.0 bar; no anisotropy was observed in the B phase at 21.0 bar. The observed behavior associated with a collective excitation of the order parameter in the B phase is shown to be qualitatively in agreement with theoretical predictions. At pressures slightly above the polycritical point some unexplained structure is observed in the velocity near the AB transition.
KeywordsSound Velocity Sound Propagation Fermi Liquid Zero Sound Lifetime Effect
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