Superfluidity of 4He Adsorbed on Nanoporous Activated Carbon Fibers

4He confined in nanoporous media is one of the most interesting nano-sized systems in the context of an interacting Bose system. In the present work, we study superfluidity of 4He adsorbed in nanoporous activated carbon fibers (ACFs). Up to a 4He coverage of n=22.6 μmol m−2, no superfluidity is observed. Over 23.7 μmol m−2, superfluid transition is observed at Tc∼550 mK. With an increase in n the superfluid density enhances, but Tc is independent of n. These observations indicate that the thickness of the superfluid 4He films on the pore wall is restricted by a slit type pore shape of ACFs.