2-DIMENSIONAL BEHAVIOR OF VERY THIN HE-4 FILMS ON GLASS

The mass-flow resistance of He-4 films on glass is investigated experi mentally by means of the well-known technique of thermally-driven coun terflow in the film-vapour system. Values of the critical film thickne ss at the onset point of superfluidity are determined accurately for t emperatures ranging from 1.00 to 2.12 K. Extensive sets of data on the flow resistance of films in the superfluid region beyond their transi tion points are collected for 1.00 K less than or equal to T less than or equal to 1.75 K. The power-law, predicted for the increase of the flow resistance with the mass-flow rate by the dynamic theory of two-d imensional films, is confirmed by the data. It is further found that t he film thickness at the onset points varies linearly with the bulk tr ansverse correlation length xi(perpendicular to)(T) over the entire te mperature range. Moreover, the variation of the exponent of the powerl aw with film thickness and temperature is found to scale with the leng th ratio x = delta(f)/xi(perpendicular to), where delta(f) is the film thickness, corrected for a temperature independent 'solid' layer of 0 .43 atomic layers. The areal superfluid density, deduced from the data , is found to increase with delta(f) almost 50% steeper than the bulkl ike growth reported in literature.