title: A new regime of nanoscale thermal transport: Collective diffusion increases dissipation efficiency.
abstract: Understanding thermal transport from nanoscale heat sources is important for a fundamental description of energy flow in materials, as well as for many technological applications including thermal management in nanoelectronics and optoelectronics, thermoelectric devices, nanoenhanced photovoltaics, and nanoparticle-mediated thermal therapies. Thermal transport at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of carrier mean free paths and energy dispersion in a material, the length scales of the heat sources, and the distance over which heat is transported. Past work has shown that Fourier's law for heat conduction dramatically overpredicts the rate of heat dissipation from heat sources with dimensions smaller than the mean free path of the dominant heat-carrying phonons. In this work, we uncover a new regime of nanoscale thermal transport that dominates when the separation between nanoscale heat sources is small compared with the dominant phonon mean free paths. Surprisingly, the interaction of phonons originating from neighboring heat sources enables more efficient diffusive-like heat dissipation, even from nanoscale heat sources much smaller than the dominant phonon mean free paths. This finding suggests that thermal management in nanoscale systems including integrated circuits might not be as challenging as previously projected. Finally, we demonstrate a unique capability to extract differential conductivity as a function of phonon mean free path in materials, allowing the first (to our knowledge) experimental validation of predictions from the recently developed first-principles calculations.
authors.affiliation: JILA and Departments of Physics and.
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Hoogeboom-Pot
authors.affiliation: JILA and Departments of Physics and.
authors.forename: Jorge N
authors.initials: JN
authors.lastname: Hernandez-Charpak
authors.affiliation: Mechanical Engineering, University of Colorado, Boulder, CO 80309; and.
authors.forename: Xiaokun
authors.initials: X
authors.lastname: Gu
authors.affiliation: JILA and Departments of Physics and.
authors.forename: Travis D
authors.initials: TD
authors.lastname: Frazer
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Erik H
authors.initials: EH
authors.lastname: Anderson
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Weilun
authors.initials: W
authors.lastname: Chao
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Roger W
authors.initials: RW
authors.lastname: Falcone
authors.affiliation: Mechanical Engineering, University of Colorado, Boulder, CO 80309; and.
authors.forename: Ronggui
authors.initials: R
authors.lastname: Yang
authors.affiliation: JILA and Departments of Physics and.
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Murnane
authors.affiliation: JILA and Departments of Physics and henry.kapteyn@colorado.edu.
authors.forename: Henry C
authors.initials: HC
authors.lastname: Kapteyn
authors.affiliation: JILA and Departments of Physics and.
authors.forename: Damiano
authors.initials: D
authors.lastname: Nardi
keywords: high harmonic generation; mean free path spectroscopy; nanoscale thermal transport; nondiffusive transport; ultrafast X-rays
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