Thermal Conductivity and Viscosity via Phonon-Phonon, Phonon-Roton and Roton-Roton Scatterings in Thin 4He Films

摘要

The coefficients of the thermal conductivity (kappa) and first viscosity (eta) in thin helium films are evaluated explicitly as a function of temperature via phonon-phonon, phonon-roton and roton-roton scatterings. Above about 0.8 K, phonon-roton scatterings and five-phonon processes are the main contributors to both coefficients. Below about 0.8 K both coefficients increase exponentially with decreasing temperature. At temperatures below 0.3 K, kappa sub ph has a T to the -5 power dependence, while eta sub ph shows exponential and 1/T dependences. In the case of eta sub ph, the former is due to phonon roton scattering and the latter originates from three-phonon processes. The coefficient kappa sub r from roton roton scattering varies as 1/T, and the roton part eta sub r of the first viscosity is independent of temperature. Keywords: Thermal conductivity; Viscosity; Phonon phonon scattering; Phonon roton interactions; Roton roton interactions; Thin helium film. (jhd)