Phonon Localization in Heat Conduction

The departure from diffusive phonon thermal transport has been extensively observed via a reduction in thermal conductivity in nanostructures. Such non-diffusive behavior has been largely explained with classical size effects, ignoring the wave nature of phonons. Here, we report localization behavior in phonon heat conduction due to multiple scattering and interference of broadband phonon waves, observed through measurements of the thermal conductivities of GaAs/AlAs superlattices with ErAs nanodots randomly distributed at the interfaces. Near room temperature, the measured thermal conductivities increased with increasing number of superlattice periods and eventually saturated, indicating a transition from ballistic to diffusive transport. At low temperatures, the thermal conductivities of the samples with ErAs dots first increased and then decreased with an increasing number of periods, signaling phonon wave localization. This Anderson localization behavior is also validated via atomistic Green’s function simulations. The observation of phonon localization in heat conduction is surprising due to the broadband nature of thermal transport. This discovery suggests a new path forward for engineering phonon thermal transport.