Kapitza Resistance Studies Using Phonon Pulse Reflection

Abstract

The transport of heat across interfaces between solids and liquid helium is generally described by a thermal boundary resistance which is named after Kapitza.¹ Two microscopic transport mechanisms have been distinguished. One is the transmission of phonons under the conservation of energy as first proposed by Khalatnikov² and later refined by many authors.³ This mechanism is very ineffective because of the large acoustic mismatch between helium and all solids. A far more effective second transport mechanism was invoked to account for the many experimental facts which were mostly obtained by phonon pulse experiments.^4–8 This mechanism was found on all surfaces studied, if the phonon frequencies were above ~50 GHz or, correspondingly, T>1K. Therefore, it was considered to be an intrinsic effect and some models were put forward which were all based on the assumption of an ideally plane surface of the solid.^9,10 None of these models was able to account at least for the magnitude of the heat transport without lumping the problem into adjustable parameters. Thus, the second heat transfer mechanism was called “anomalous”, and was considered to be - if not miraculous - a tantalizing problem at least.¹¹