The Kapitza Resistance of Metals in the Normal and Superconducting States

A calculation has been made of the transfer of heat across a metal-liquid helium interface. In the normal state an appreciable transfer of energy occurs directly from the conduction electrons to the phonons of the fluid. Three mechanisms have been considered: the phonon-electron interaction within the metal, the modulation of the position of the interface and the phonon-electron interaction of the electrons which have tunnelled into the helium. All appear to be important. In the superconducting state each of these becomes ineffective at temperatures appreciably below the transition temperature and, consequently, the heat flow is reduced. The effect is sensitive to band structure and to the anisotropy of the energy gap.