Size effects in He II as measured by fourth sound

Abstract

Fourth-sound measurements are used to determine the depletion in the superfluid density ρs which occurs in the helium filled small pores of packed powders. The measurements also give the reduction in superfluid onset temperature. The pore size distribution of several samples was determined from desorption isotherms. Using this distribution and an independent pore model, calculations based on the Ginzburg-Pitaevskii ansatz with a healing length first proposed by Mamaladze are found to be in good agreement with experimental results in several cases. The superfluid onset temperature seems to be determined by the average pore size. Fourth-sound measurements as a function of temperatureT in large pore geometries accurately give ρs ∼ (Tλ −T)2/3 in the neighborhood of the lambda temperatureTλ.