Transition from population- to coherence-dominated nondiffusive thermal transport

Abstract

Deviations from diffusive heat transport in high thermal conductivity crystalline insulators are generally understood within the framework of the phonon Boltzmann Transport Equation. However, for low thermal conductivity materials with large primitive cells or strong anharmonicity, the recently developed Wigner Transport Equation is more appropriate as it includes tunnelling between overlapping phonon bands. In this work, via solutions to the Wigner Transport Equation, we develop a scheme to obtain the dynamics of the phonon populations and coherences as a function of an arbitrary heat source. The approach is applied to predict size effects and dynamical thermal conductivities in CsPbBr${}_{\text{3}}$ and La${}_{\text{2}}$Zr${}_{\text{2}}$O${}_{\text{7}}$ using first-principles data as input. We predict significant deviations from the bulk thermal conductivity in these materials at length scales on the order of hundreds of nanometers to a few microns at room temperature, well within the reach of direct observation using current experimental techniques.

9 pages, 3 figures

References in corpus (9)

• Implementation strategies in phonopy and phono3py
• Unified theory of thermal transport in crystals and disordered solids
• Direct Measurement of Room Temperature Non-diffusive Thermal Transport Over Micron Distances in a Silicon Membrane
• Observation of second sound in graphite at temperatures above 100 K
• Ab initio variational approach for evaluating lattice thermal conductivity
• Thermal transport in crystals as a kinetic theory of relaxons
• Improved Callaway model for Lattice Thermal Conductivity
• Unifying first principle theoretical predictions and experimental measurements of size effects on thermal transport in SiGe alloys
• Ultrafast Electron Diffuse Scattering as a Tool for Studying Phonon Transport: Phonon Hydrodynamics and Second Sound Oscillations