Superfluidity of ⁴He confined in a porous glass and control of the pore size

⁴He confined in nanoporous media is one of the most interesting nano-sized systems. The aim of the present work is control of the pore size of nanoporous media in order to clarify the superfluid size effects. For the pore size control, monolayer adsorption of Kr on the pore wall is performed. The change in the pore size distribution by the monolayer adsorption are characterized by N ₂ isotherms at 77 K. Superfluidity in the pores is observed with a torsional oscillator method. The pore diameter of the as-purchased Gelsil is estimated at 5.8 nm. The monolayer adsorption reduces the size by 1.1 nm, caused by the thickness of the Kr monolayer. The decrease in the pore size lowers the superfluid transition temperature by 40 mK.