Vortices, Superfluidity and Phase Transition in 4He Film Adsorbed on Porous Materials

Abstract

We investigate the superfluid transition of 'He thin film adsorbed on porous materials with emphasis on the role of vortices. Considering the multi· connectivity of the film, we show that the interaction among the vortices excited in the film is essentially one dimensional due to the quantum behavior of the flow. As a result, it is generally shown that the vortices do not dissociate at TA where the long range order (LRO) vanishes in contrast to the two dimensional case. We also study the mechanism of dissipation for applied AC flow with the frequency (J), noting that a finite dimension of the film, the pore size a, plays an important role. The crossover phenomena between the Kosterlitz- Thouless transition and the I! transition are predicted: The superfiuid onset is accompanied with the disappearance of the free vortices in large a or high (J) cases, whereas with the appearance of the LRO in small a or low (J) cases. Our theory qualitatively explains various experimental results with the torsion pendulum.