Our experimental setup consists of a brass cylinder filled with liquid helium. A fine superconducting wire is stretched along the cell, displaced from the cylinder's axis. If the wire serves as the core of a superfluid vortex, its vibrational normal modes change. A vortex can also be partially attached, with its core running along a portion of the wire, then traversing the fluid as a free vortex.

By measuring the vibration frequencies, we find what fraction of the wire is covered by vortices. If there is a partially attached vortex, its free end precesses around the cell, driven by the flow field of the trapped portion. Since the wire is off-center, the location of the attachment point oscillates during the precession to conserve energy. We then detect the motion of the attachment point as a change in the measured beat frequency, and reconstruct the motion of the free vortex segment.

We can explore details such as the vortex behavior as it pins to bumps on the container wall. Our data also shows that pinning occurs more easily as temperature increases, the reverse of the usual temperature dependence found in superconductors.

Here are elementary discussions (with pictures) of superfluid helium, superfluid vortices, and our helium measurements.

Recent papers:

R.J. Zieve and L.A.K. Donev, ``Stable Vortex Configurations in a Cylinder," cond-mat/0006078, and J. Low Temp. Phys. 121, 199 (2000).

L.A.K. Donev, L. Hough, and R.J. Zieve, ``Depinning of a superfluid vortex line by Kelvin waves," cond-mat/0010240, and Phys. Rev. B 64, 180512 (2001).