Also found in: Wikipedia.
a special kind of wave that can be propagated in quantum fluids or, more precisely, Fermi fluids, such as liquid He3, at temperatures very close to absolute zero. It is associated with the departure of the distribution function of the elementary excitations, or quasiparticles, existing in a Fermi fluid from the equilibrium value. The speed of zero sound c0 is not the same as the speed of ordinary sound c, which is dependent on the compressibility of the fluid, and indeed c0 > c. The existence of zero sound was predicted by L. D. Landau in 1957 on the basis of the general theory of Fermi fluids. Zero sound was observed experimentally in liquid He3 by the American physicists W. Abel, A. Anderson, and J. Wheatly in 1966. In the temperature range from 0.002° to 0.1° K at a pressure of 0.32 atmosphere, the average value of c was 187.9 m/sec, while c0 was 194.4 m/sec (at frequencies of 15.4 and 45.5 megahertz). Under certain conditions, zero sound can also exist in metals where the electrons form a charged Fermi fluid.