Rotation-induced three-dimensional vorticity in He4 superfluid films adsorbed on a porous glass

A detailed study of torsional oscillator experiments under steady rotation up to 6.28rad sec is reported for a He4 superfluid monolayer film formed in 1-μm-pore-diameter porous glass. We discovered a new dissipation peak, whose height changes in proportion to the angular speed. The new peak appears at a temperature lower than the vortex pair unbinding peak observed in the static state. A model of three-dimensional (3D) coreless vortices ("pore vortices") is proposed to explain this additional peak in terms of 2D vortex pair dynamics in the presence of a flow field caused by 3D vortices. The new peak originates from dissipation close to the pore vortex lines, where a large superfluid velocity shifts the vortex pair unbinding dissipation to lower temperature. This explanation is consistent with the observation of nonlinear effects at high oscillation amplitudes.