Fundamental Study of Vortex State using Mono-layer superfluid Heliumu Films formed in Porous Media

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We have studied 3D superfluid made from an ideal 2D system, a superfluid made of ^4He mono-atomic-layer film formed on a solid surface. We know such a system undergoes a typical 2D superfluid transtion, KT transition if the surface is fiat. When the ^4He mono-atomic-layer is formed on a surface which is interconnected 3D wise, we may expect a 3D phase transition. We have made an extensive experimental study utilizing very sensitive torsional oscillators to study this superfluidity and vortices in such 3D connected ^4He mono-atomic-layer films. We have used our unique rotating cryostat for experiments under rotation. The followings are the major results:1].3D vortices core size has been derived from the detailed study of 3D superfluid density in the absolute unit, namely (kg/m^3) using the Josephson's relation. The result is compared with the 2D vortex core size of 25 □ and actually 3D core is always a few times larger than the pore diameter of the substrate.2].Vortex lines threading through the substrate are expected to be produced in the 3D superfluid. Our recent result shows the first clear experimental evidence of 3D vortices created under steady rotation. An energy dissipation peak originates from 2D vortices in a KT films near transition temperature. The 3D system made of He films condensed on 3D connected surface now produce 3D vortices and the superfluid velocity field induced by the 3D vortices induce extra energy dissipation.3].Superfiow through the 3D superfluid made of ^4He mono-atomic-layer film is further a good tool to study this unique system. Newly introduced continuously operable refrigerator now is ready for such kind of experiments using superflow.