Atomistic modeling of extreme near-field heat transport across nanogaps between two polar dielectric materials
Yangyu Guo, Mauricio Gómez Viloria, Riccardo Messina, Philippe Ben‐Abdallah, Samy Mérabia
Abstract
The understanding of extreme near-field heat transport across vacuum nanogaps between polar dielectric materials remains an open question. In this work, we present an investigation of heat transport across vacuum nanogaps between magnesium oxide (MgO) surfaces by nonequilibrium molecular dynamics (NEMD) simulation, which naturally accounts for the nonlocal dielectric response from both acoustic and optical branches as well as phonon tunneling. A consistent comparison is also made with the continuum fluctuational electrodynamics theory using both local and nonlocal dielectric functions computed by equilibrium molecular dynamics with the anharmonic damping properly included. As a result, the direct NEMD result shows significant deviations from the continuum theory even up to a gap size of a few nanometers. The lattice anharmonicity is demonstrated to have a large impact on the energy transmission and thermal conductance, in contrast to its moderate effect reported for metallic vacuum nanogaps. The present work thus provides further insight into the physics of heat transport in the extreme near-field regime between polar materials, and puts forward a methodology to account for anharmonic effects.