Singularity and nonlinearity in the Kapitza resistance between gold and superfluid 4He near Tλ

We report experimental results for the Kapitza resistance RK between gold and superfluid 4He, which were obtained by using very-high-resolution thermometry. The data imply that RK is singular at the superfluid transition temperature Tλ. Comparison with theory suggests that the singularity results from a hydrodynamic effect proposed by Landau, and that it is associated with the vanishing of the superfluid and normal-fluid currents at the boundaries. Recently a quantitative prediction of the singular part of this Kapitza resistance has been made based on dynamic renormalization-group theory. This theory requires no adjustable parameters and it agrees well with our data. The measurements of RK are independent of the heat flux Q only for reduced temperatures t=1-T/Tλ greater than a characteristic value tc. We find that tc is approximately proportional to Q, and that for t<tc the maximum value of (∂RK/∂Q)t is approximately proportional to 1/t. The Q-dependent contribution RKQ to RK can be represented by a function of the single variable Q/t. For large Q/t, this function saturates at a value near 0.35 cm2 K/W. We know of no theory that predicts the dependence of RK on Q