Mutual Friction in Superfluid 4He Near the λ-Line

Abstract

We present experimental results for the thermal resistivity ρ of superfluid ⁴He along several isobars between saturated vapor pressure and the melting pressure. The measurements are for the temperature range 1−T _c(q)/T _λ<t<2×10⁻⁵ and the heat-flux range 3<q<70 μW/cm². Here t≡1−T/T _λ, T _λ is the transition temperature in the limit of zero q, and T _c is the transition temperature at finite q. The data suggest that the resistivity has an incipient singularity at T _λ which can be described by the power law ρ=(t/t ₀)^−(mν+α) where t ₀=(q/q ₀)^x. However, the singularity is supplanted by the transition to a more highly dissipative phase at T _c(q)<T _λ. The results suggest a mild dependence of mν+α on the pressure P, but can be described quite well by mν+α=2.76, x=0.89, and q ₀=q _0, 0−q _0, 1 P with q _0, 0=401Wċcm⁻² and q _0, 1=−5.0Wċcm⁻²bars⁻¹. The results imply that the Gorter–Mellink mutual friction exponent m has a value close to 3.46 and is distinctly larger than the classical value m=3.