Effect of the Gravitational Field on the Superfluid Transition inHe4

Abstract

It is shown experimentally that in a liquid helium sample of finite height, He II and He I coexist in thermodynamic equilibrium over a finite temperature range. This is contrary to a recent theoretical prediction. Observations made by noting the position of the boundary between the phases of high and low thermal conductivity as a function of temperature are quantitatively confirmed by high-resolution heat-capacity measurements near the transition region. The rate of movement with temperature of the interface between the two phases yields a slope for the transition line of 113.9±4.6 atm/°K at saturated vapor pressure, in quantitative agreement with recent direct measurements.