SINGULARITY AND NONLINEARITY IN THE KAPITZA RESISTANCE BETWEEN GOLD AND SUPERFLUID HE-4 NEAR T-LAMBDA

We report experimental results for the Kapitza resistance R(K) between gold and superfluid He-4, which were obtained by using very-high-resolution thermometry. The data imply that R(K) is singular at the superfluid transition temperature T-gamma. 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 R(K) are independent of the heat flux Q only for reduced temperatures t = 1 - T/T-gamma greater than a characteristic value t(c). We find that t(c) is approximately proportional to Q, and that for t < t(c) the maximum value of partial-R(K)/partial-Q)t is approximately proportional to 1/t. The Q-dependent contribution R(KQ) to R(K) 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 R(K) on Q.