| 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: |