Polarization of Vortex Pairs in Rotating Superfluid Films

The free energy of vortex-antivortex pairs in a rotating superfluid film is calculated using standard two-fluid hydrodynamics. A term is found proportional to the rotation rate, the distance of the pair from the rotation center, and the cosine of the angle between the pair impulse vector and the azimuthal rotation direction. This means that the pairs will become polarized by the rotation, with the pairs lining up such that they contribute a net dc current in the azimuthal direction. Our results contradict a claim by Adams and Glaberson (Phys.Rev. B 35, 4633 (1986); J. Low Temp. Phys. 67, 103 (1987)) that the pairs are unaffected by rotation. For temperatures close to the Kosterlitz-Thouless transition where the pair density becomes large, the lowered free energy of the pairs in rotation could possibly give rise to extra torsion oscillator attenuation below T_KT, as seen in the Adams-Glaberson experiment.