Role Of Phonon Coupling And Non-Equilibrium Near The Interface To Interfacial Thermal Resistance: The Multi-Temperature Model And Thermal Circuit

Interfacial thermal transport between two semi-infinite leads has been widely assumed to be independent from bulk transport in the two leads. However, here we show that due to the mismatch of phonon modal interfacial conductance and modal thermal conductivity, thermal interfacial transport is affected by the bulk thermal transport, and phonons near the interface can be driven into strong non-equilibrium, causing an additional resistance that is lumped into the interfacial resistance. This is captured using a multi-temperature model (MTM) that we introduce. Using thermal properties predicted from first-principles calculations and interfacial transmission coefficients predicted from the acoustic mismatch model, we present a case study of thermal transport across the Si-Ge interfaces using our MTM. The results show that phonon branches are in non-equilibrium near the interface due to energy re-distribution caused by different thermal properties of the materials and the corresponding transmission coefficients, and the overall interfacial thermal conductance is 5.4% smaller than the conventional prediction, due to the phonon non-equilibrium resistance. We present a thermal circuit to include this new resistance due to phonon-phonon coupling and non-equilibrium near the interfaces. The thermal circuit also shows that increasing the phonon-phonon coupling factor Gpp can reduce this resistance. Our MTM is a general and simple analytical approach expected to be useful for investigating the coupling between thermal transport across interfaces and in the bulk leads. Published under license by AIP Publishing.