Temperature Dependence of Superfluid Critical Velocities NearTλ

Persistent-current methods are used to obtain critical-velocity data for flow of superfluid helium through filter materials with uniform pore size. For the smallest pore size investigated, 0.2μ, evidence is seen for a small depression (7.5×${10}^{-4\mathrm{}}$°K) of the transition temperature. The critical velocity for this pore size is found to vary linearly with the superfluid density as the transition temperature is approached.