The viscosity and acoustic impedance of liquid helium-3

Abstract

Previous experiments have shown that at low temperatures the acoustic impedance of liquid 3 He under the saturated vapour pressure rises by about 10% below about 0.092 °K. This rise is predicted by Landau’s theory of a Fermi liquid. It comes about because, at sufficiently low temperatures, sound waves in liquid 3 He are propagated as a new mode, the so-called zero sound. The present experiments study the dependence on pressure of the temperature and magnitude of the transition in the impedance. The transition temperature is shifted from 0.092 to about 0.07 °K on subjecting the liquid to a pressure of 12.5 atm, and the magnitude of the change considerably reduced. To interpret these results, measurements have also been made of the viscosity as a function of pressure. (These give information about the thermal relaxation times in the liquid.) All the results are in accord with the theory of zero sound in a Fermi liquid.