Non-equilibrium transport and phonon branch-resolved size effects based on a multi-temperature kinetic model

TL;DR

This paper introduces a multi-temperature kinetic model for non-equilibrium transport in graphene, capturing phonon branch-specific effects and size-dependent thermal conductivity without assuming diffusive phonon transport.

Contribution

It develops a novel kinetic model that accounts for branch-dependent electron-phonon interactions and free phonon migration, improving understanding of nanoscale thermal transport in graphene.

Findings

ZA phonon branch dominates thermal conduction.

Thermal conductivity varies with system size and position.

ZA branch can exceed lattice thermal conductivity at nanoscale.

Abstract

Non-equilibrium transport and phonon branch-resolved size effects in single-layer graphene materials are studied under a multi-temperature kinetic model, which is developed for capturing the branch-dependent electron-phonon coupling. Compared with typical macroscopic multi-temperature models, the assumption of diffusive phonon transport is abandoned in this model and replaced by the free migration and scattering of particles. The phonon branch- and size-dependent effective thermal conductivity is predicted in nanosized graphene as well as the temperature slips near the boundaries. Compared with other phonon branches, the ZA branch contributes the most to thermal conduction regardless of system sizes. Furthermore, in nanosized homogeneous graphene with a hotspot at the center, the branch-dependent thermal conductivity increases from the inside to the outside even if the system size is fixed. The thermal conductivity of ZA branch is even higher than the lattice thermal conductivity when the system size is hundreds of nanometers.