Determining phonon mean free paths from observations of quasiballistic thermal transport.

The mean free paths (MFPs) of thermal phonons are mostly unknown in many solids. Recent work indicates that MFPs may be measured using experimental observations of quasiballistic thermal transport, but the precise relationship between the measurements and the MFP distribution remains unclear. Here, we present a method that can accurately reconstruct the MFP distribution from quasiballistic thermal measurements without any assumptions regarding the phonon scattering mechanisms. Our result will enable a substantially improved understanding of thermal transport in many solids, particularly thermoelectrics.