AQP Seminar: Crossover between electron-phonon and boundary resistance limited thermal relaxation in copper films

Aalto Quantum Physics Seminar (Nanotalo). Speaker: Libin Wang (Pico, Aalto)

For a heated normal metal film on a dielectric substrate, energy is dissipated as a whole mainly by electron-phonon (ep) coupling to the film phonons, characterized by ep thermal coupling resistance Rep. Film phonons are coupled with substrate phonons by phononic coupling and the corresponding thermal boundary resistance is Rpp. The energy relaxation of electrons in the metal films determined by Rep and Rpp, with the weaker of the two dominating the energy relaxation process.

In this talk, we will show the crossover between electron-phonon and boundary resistance limited thermal relaxation in copper films at sub-kelvin temperatures. The latter mechanism will dominate the energy relaxation at a temperature well below the theory predicted. The thermal boundary resistance between the copper film and the substrate is measured directly from the experiments. We show that by adding a third layer of film between the copper film and the substrate, the thermal boundary resistance is increased fourfold, consistent with an assumed series connection of the thermal resistances.

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