Kapitza resistance between silver films and liquid helium-3 below 50 millikelvin

The Kapitza resistance between 5000-Angstrom silver films and liquid 3He is measured over the temperature range 3 to 45 mK. The silver films are vapor-deposited onto both sides of a microscope cover glass and are smooth down to at least 1000-Angstrom scales. The temperature of the silver films is measured by tracking the capacitance of the underlying cover glass, and the temperature of the 3He is measured with a melting curve thermometer. For temperatures above 30 mK, Rk ∝ T-3, and the heat transport is dominated by phonons. For temperatures below 15 mK, Rk diverges more slowly, with a temperature exponent closer to -1. A magnetic field dependence is seen in this temperature regime. At a constant temperature of 6.7 mK, Rk has a minimum as a function of magnetic field strength. The position of the minimum, observed at H ∼ 25 gauss, corresponds to μBH/kβT ∼ 1/4. This is close to many theoretical predictions that attribute major heat transport to the magnetic dipole coupling between the nuclear spins of the 3He quasiparticles and the localized electron spins on the solid surface. For temperatures between 15 and 30 mK, Rk ∝ T-2 and has no magnetic field dependence. A dependence of Rk, on liquid 3He pressure is seen, however, over the entire temperature range of the experiment. From 0 to 10 bars, Rk is inversely proportional to m*(P), the effective mass of liquid 3He, i.e., Rk(T,P)m*(P) is independent of pressure. This observation cannot be explained by existing theories. Finally, for temperatures below 30 mK, where magnetic heat transport is important, some increase in Kapitza resistance is observed following thermal cycling