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Helium in nanoporous media has attracted much interest as a model Bose systemwith disorder and confinement. Here we have examined how a change in porousstructure by preplating a monolayer of krypton affects the superfluidproperties of $^4$He adsorbed or confined in a nanoporous Gelsil glass, whichhas a three-dimensional interconnected network of nanopores of 5.8 nm indiameter. Isotherms of adsorption and desorption of nitrogen show thatmonolayer preplating of Kr decreases the effective pore diameter to 4.7 nm andbroadens the pore size distribution by about eight times from the sharpdistribution of the bare Gelsil sample. The superfluid properties were studiedby a torsional oscillator for adsorbed film states and pressurized liquidstates, both before and after the monolayer Kr preplating. In the film states,both the superfluid transition temperature $T_{\mathrm c}$ and the superfluiddensity decrease about 10 percent by Kr preplating. The suppression of filmsuperfluidity is attributed to the quantum localization of $^4$He atoms by therandomness in the substrate potential, which is caused by thepreplating--induced broadening of the pore size distribution. In thepressurized liquid states, the superfluid density $\rho_{\mathrm s}$ is foundto increase by 10 percent by Kr preplating, whereas $T_{\mathrm c}$ isdecreased by 2 percent at all pressures. The unexpected enhancement of$\rho_{\mathrm s}$ might indicate the existence of an unknown disorder effectfor confined $^4$He.

Suppression of Superfluidity of $^4$He in a Nanoporous Glass by Preplating a Kr Layer