THERMAL RESPONSE OF A HE-3-SUPERFLUID-HE-4 MIXTURE

The response of a layer of superfluid mixture to an ac heat source, Q(t)=Q0 exp (iωt), is determined. In the low-frequency regime, the temperature response at the heated side of a superfluid layer is essentially identical to that of an ordinary fluid having a thermal conductivity κeff and a thermal diffusion coefficient Γ0/2. Here κeff is the effective conductivity of Khalatnikov, and Γ0 is the diffusion coefficient of Griffin. At much higher frequencies, the results are more complicated. The low-frequency regime is defined in terms of the second sound velocity u2 by ω≪u22/Γ0. The ac response function is valuable in a number of ways. It can be used to obtain the system response to more complicated time-dependent variations in Q such as step changes in Q. A knowledge of the response function in the low-frequency regime provides a mechanism for directly determining the Kapitza resistance in mixtures. Finally, a knowledge of the response function provides an additional opportunity to test two-fluid hydrodynamics. Alternative tests of superfluid hydrodynamics are of particular interest in light of recent experiments that show anomalous values for κeff in the low3He concentration limit © 1990 Plenum Publishing Corporation.