Superfluid film

There has been a tremendous amount of work done in the field of phase transitions and critical phenomena in two dimensions.

The 2D XY model - where the order parameter is characterized by an amplitude and a phase - is the universality class for this transition.

In looking at phase transitions in thin films, specifically helium, the two main experimental signatures are the superfluid fraction and heat capacity.

This results in a multiply connected film where the substrate is much like Swiss cheese with the holes interconnected.

A third method is to separate two extremely flat plates by a thin spacer, again resulting in a large surface area to volume ratio.

An early design of torsional oscillator was first used by Andronikashvili to detect superfluid in bulk fluid 4He, and later modified by John Reppy and co-workers at Cornell in the 1970s.

[further explanation needed] Therefore, lowering the moment of inertia reduces the resonant period of the oscillator.

A typical set of data clearly showing the superfluid decoupling in helium films is shown in ref.

To probe theories of dynamical aspects of thin film phase transitions one must use an oscillator with a much higher frequency.

[4] The KT theory has been confirmed in a set of experiments by Bishop and Reppy in planar films, i.e.