A new regime of nanoscale thermal transport : collective behavior counteracts dissipation inefficiency

Understanding thermal transport from nanoscale hot spots is important for a fundamental description of energy transport in materials, as well as many technological applications including thermal management in nanoelectronics, thermoelectric devices, nano-enhanced photovoltaics and nanoparticle-mediated thermal therapies. Heat transfer at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of phonon mean free paths 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 (valid at the bulk and continuum levels) dramatically over-predicts 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 interplay between neighboring heat sources can facilitate efficient, diffusivelike heat dissipation, even from the smallest nanoscale heat sources. This finding suggests that the thermal management problem in nanoscale systems including integrated circuits might not be as serious as projected. Finally, we demonstrate a unique and new capability to extract mean free path distributions in materials, allowing the first experimental validation of differential conductivity predictions from first-principles calculations.