Phonon hydrodynamic transport in bilayer graphene

This study investigates the hydrodynamic characteristics of phonon-mediated thermal transport in bilayer graphene (BLG) through direct numerical simulations of the phonon Boltzmann transport equation, coupled with ab initio calculations. We systematically analyze size-dependent effects on in-plane thermal transport and provide a theoretical prediction for the Knudsen minimum phenomenon, which occurs at a characteristic width of approximately 1 mu m and a temperature of 100 K. Additionally, the impact of edge surface roughness on hydrodynamic transport is explored, revealing that smoother boundaries reduce phonon boundary scattering and suppress hydrodynamic effects. Our results further show that excessively short ribbon lengths hinder hydrodynamic phonon transport in rectangular ribbons, preventing the observation of the phonon Knudsen minimum. The absence of this phenomenon in short ribbons emphasizes the critical role of ribbon length in facilitating hydrodynamic regimes. These findings offer a comprehensive understanding of the interplay between geometric constraints and phonon scattering mechanisms in phonon-mediated thermal transport in BLG. This work provides a robust theoretical framework and valuable insights for experimental studies on phonon hydrodynamic transport in BLG.