Specific Heat and Superfluid Density of Liquid Helium in Porous Media

An experimental and theoretical investigation of liquid helium confined to the small pores of highly compressed powders was carried out in order to investigate size effects in liquid helium. The specific heat measurements show that the bulk specific heat singularity is replaced by a flattened peak that is shifted towards lower temperatures with decreasing pore size. The superflow onset temperature and the superfluid fraction rho(s)/rho were determined from fourth-sound measurements in the same powders in which specific heat measurements were made. The onset temperature and the temperature of the specific heat peak were found to be equal within experimental error. The Ginzburg-Pitaevskii model was used to calculate the specific heat of liquid helium in finite systems.