Persistent currents and critical velocities in 3He--4He mixtures

Using the method of Doppler-shifted fourth sound, an investigation is made of the angular velocity omega/sub c1/ for the onset of vorticity, the saturated critical velocity, and the dependence of rho/sub s//rho on v/sub n/--v/sub s/ for 4He in three different pore sizes and for three different mixtures of 3He-4He in one of the powders used. These are the first measurements of critical velocities in 3He-4He mixtures. A weak dependence of ω/sub c1/ on the pore size and within the limits of the experiment no dependence on concentration X up to X = 0.11 is observed. It is found, however, that the maximum v/sub n/-v/sub s/ attainable increases as the concentration of 3He increases for X less than or equal to 0.17. The observed dependence of the superfluid density on v/sub n/-v/sub s/ is approximately two orders of magnitude stronger than predicted