Vortex confinement in superfluid films on porous media

Abstract

Vortex-vortex interactions in superfluid 4He films adsorbed on porous media are investigated by taking the multiple connectivity of the surface explicitly into account. It is shown that point vortices are “confined” by a quantum effect, which produces a phenomenological picture in which tightly bound pairs (called “vortex molecules”) are interacting with a long range potential. As a result, the superfluid transition is not associated with point vortex pair unbinding in contrast to the way that Kosterlitz and Thouless suggested, but with an anomalous behavior of the molecules.