COLLECTIVE OSCILLATIONS IN He3-He4 MIXTURES.
Research Communication no. 69,
DOUGLAS AIRCRAFT CO INC HUNTINGTON BEACH CALIF ADVANCED RESEARCH LABS
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The existence of collisionless phonons in He3-He4 mixtures is predicted on the basis of a self-consistent field calculation. The phonon velocity is calculated for all temperatures over the region 0 0 1.5K and for all molar concentrations of He3. The velocity is found to increase monotonically with increasing temperature for all molar concentrations. Significantly, the behavior of these excitations is not overtly sensitive to the state of the superfluid. It is argued that the phonon excitation of pure He4 and the zero-sound mode of pure He3 belong to the same branch and evolve continuously into one another as the fractional concentration of He3 in the mixture changes from zero to unity. The differential inelastic X-ray scattering cross section is also calculated for the mixture. Author