Experiments on the superfluid circulation in rotating helium II

Experimental observations have been made of the magnitude and direction of the superfluid circulation around a fine wire in a rotating vessel filled with He II, by means of the Vinen method. Measurements were made using wires from 66 to 83 μm in diameter at temperatures from 1.23 to 1.35 degreeK with angular velocities of rotation in the range between plus-or-minus4 rad sec-1. At any given rotational angular velocity, the circulation was observed to be metastable over a continuous range of values between certain limits which lay several quantum units apart and which varied with angular velocity. Direct evidence for quantization of circulation is lacking in these observations as a result of the metastability encountered. However, the general trend of the metastable values of circulation as a function of rotational angular velocity is in accord with the predictions of simple minimum-free-energy arguments for the dependence of the true equilibrium value of circulation upon angular velocity