Landau state - Vortex-Free State of He-B in a Rotating Cylinder

Using the knowledge on vortex pinning acquired in the first series of experiments on rotating superfluid 3He, it was possible to create vortex-free states up to 1 rad/s in a 5-mm-diameter cylinder filled with 3He-B [PRL 59, 1006 (1987)]. This observation proved that there is a fundamental difference between 3He and 4He superfluids: the vortex creation is more difficult in 3He than in 4He owing to the macroscopic vortex core on the order of 100 Å. The 3He superfluid is theoretically more tractable than its 4He counterpart and, therefore, these findings have stimulated substantial new interest in the problem of vortex creation in superfluids.


FIGURE Two sequences of NMR spectra recorded at 29.3 bar pressure  and at 0.65Tc, as a function of magnetic field in (a) one direction of rotation and in (b) the opposite direction. The large changes in the NMR response are due to counter-flow-induced textural changes in the cylindrical sample with a flare-out texture in the stationary state. A clear asymmetry is observed in these experiments, similar to a  gyromagnetic effect.
 
We have investigated vortex-free counterflow states in He-3 at 29.3 bars in a rotating cylinder of radius R =2.5 mm; cw NMR at 923 and 1653 kHz was used. The experimental volume was similar to that in many of our previous experiments,  except that the height of the cylinder was reduced by 5 to 25 mm and a Mylar diaphragm,with a 1.5-mm hole, was installed to separate the cylinder from the heat-exchanger volume (D=30 mm). The diaphragm increased the critical angular velocity for vortex formation from the previously measured value of 0.1-0.2 rad/s to 0.4-0.5 rad/s at 284 Oe and to 0.9 rad/s at 504 Oe. Thus, vortices created below the diaphragm in the heat-exchanger volume did not move freely through the 1.5-mm hole to fill the sample volume.

The measured cw NMR spectra, reflecting the order-parameter structure, responded very differently to rotation in opposite directions. The sign of this asymmetry was not linked to the direction of the applied magnetic field, as expected for a true gyromagnetic effect, but it varied randomly from one cooldown to another.
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