5) Vortices in Rotating Superfluid 3He

The superfluid state, in general, is characterized by frictionless, highly correlated irrotational motion of the fluid particles. The superfluid accommodates to rotation by forming a lattice of quantized vortices in which the vortex core, typically singular, breaks the topological constraint against rotational motion. In superfluid 3He, the structure of vortex cores can be much more complicated than in conventional superfluids because of the many degrees of freedom provided by the 18-dimensional order parameter manifold.

The work on superfluid 3He in rotation was commenced in 1978 when the design of a nuclear demagnetization cryostat was initiated at the Low Temperature Laboratory of the Helsinki University of Technology; I joined the construction work in 1979. The cryostat, the first of its kind combining millikelvin techniques and an air bearing system, was completed in the end of 1981. At the time of the first experiments, performed using nuclear magnetic resonance techniques, no striking results were expected since vortex cores were thought to be too small to leave an imprint on the absorption spectra. However, this proved to be false and several fundamental findings on vortices in rotating superfluid 3He were obtained in these experiments:

   - Evidence for vorticity in superfluid
3He-A  [PRL 48, 1838 (1982)]
   - Continuous vortices in superfluid 3He-A  [PRL 49, 1258 (1982)]
   - Magnetic vortices in rotating 3He-B  [PRL 51, 1362 (1983)]
   - Vortex core transition in superfluid 3He-B  [PRL 53, 584 (1984)]
   - A-phase vortices in 10 micron gaps  [PRL 58, 678 (1987)]
   - Landau state in superfluid 3He-B  [PRL 59, 1006 (1987)]