THERMAL CONDUCTANCE STUDY OF THIN SUPERFLUID FILMS FORMED IN POROUS-GLASS WITH 1-MICROMETER PORE DIAMETER

In order to study the combined nature of 2D and 3D superfluidity a,nd the vortex state in thin He-4 films formed in porous glasses superflow properties are studied using effective thermal conductance measuremen ts, Detailed study, though still preliminary, reveals quite different features from 2D superfluidity or that of bulk one. For the film with Tc=670 mK, we observe a change of the superflow properties, below 600 mK and when a critical flow velocity is exceeded. This transition is c haracterized by appearance of quite a long time constant and is indica tive of formation of new vortex state. Films with Tc=1015, 1130, 1276 mK do not have this long ti:me constant over the studied velocity, or dQ/dt range for the temperature above 500 mK.