Understanding phonon spatial coherence via atomistic wave-packet simulations

Principally, phonons exist as propagating wave-packets. In most situations, the transport and interactions of the propagative phonons can be accurately described as particle-like. However, some artificially structured materials can stimulate the phonons to physically behave like waves in a phenomenon known as phonon spatial coherence. This typically occurs when the average distance between heterogeneous scatterers in the solid is less than the spatial extensions of the phonon wave-packets, allowing for significant constructive wave interference that changes the properties of the phonons to transport like waves relative to the artificial structure. Manipulation of wave-like phonon behaviors through mechanisms such as Anderson localization can result in thermal conductivity extremes beyond the particle-based methods for engineering thermal transport. In this talk, we discuss how atomistic wave-packet simulation, through its unique capability to directly model the transport of phonon wave-packets, has enabled discovery and novel analyses of many aspects of the spatial coherence phenomenon. We specifically highlight our own investigations regarding the low-dimensional superlattice, a metamaterial consisting of periodically alternating layers of two or more materials.