Fm. Ellis et al., PINNED VORTEX DENSITY IN HE-4 FILMS PRODUCED AND DETECTED BY 3RD-SOUND RESONANCES, Physica. B, Condensed matter, 194, 1994, pp. 673-674
Resonant frequencies in a circular third sound resonator are shifted b
y DC persistent current flow fields present in the resonator. Each mod
e is shifted differently according its ''overlap'' with the flow. Meas
urements of these shifts consequently reflect the flow field, and henc
e the distribution of vortices. In addition, large amplitude circularl
y polarized third sound modes are used to create and destroy the flow
states. Several conclusions can be drawn from the experiments: 1) Vort
ex densities of hundreds of thousands per square centimeter exist in q
uasi-equilibrium; 2) Vortex distributions include large densities of b
oth circulation senses polarized to different radii within the cell; 3
) Pinning strengths are consistent with the bulk pinning model of Schw
arz1 applied to a film; and 4) Third sound amplitudes with AC flows ap
proaching the Feynman critical velocity create new vorticity. These re
sults offer validity to the hypothesis that pinned vortices are a perv
asive feature of superfluid films at low temperatures.