Thermal boundary resistance between liquid helium and silver sinter at low temperatures

Abstract

We present measurements of the thermal coupling between Ag sinter (nominal grain size ≈ 700 Å) and superfluid3He-B atp = 0.3, 10, and 20 bar as well as a phase-separated3He4-He mixture atp = 0.5 bar in the submillikelvin regime. In order to analyze the data of the pure3He-B sample with respect to different contributions to the thermal resistance, a one-dimensional model for the heat flow in the sinter is presented. As a result it is shown that the thermal conductivity of the liquid in the sinter has to be taken into account to extract the temperature and pressure dependence of the boundary resistance in the confining geometry of the sinter. Depending on the value of this thermal conductivity, a boundary resistance proportional toT −2 orT −3 is found. Moreover, it is shown that a pressure dependence of the boundary resistance might be explained by a pressure dependence of the thermal conductivity of the liquid in the sinter. The data on the phase-separated mixture are equally well described by aT −2- and aT −3-dependence of the boundary resistance. We point out that a common problem in most measurements of the Kapitza resistance performed so far is the small temperature interval investigated, which usually does not allow a definite conclusion concerning the temperature dependence.