Transient hydrodynamic phonon transport in two-dimensional disk geometry

Abstract: Transient cooling phenomenon in two-dimensional materials is studied based on the phonon Boltzmann transport equation (BTE). Using a heating laser pulse to heat the two-dimensional disk geometry under the environment temperature, after the heating laser is removed, our results show that the transient temperature could be lower than the environment temperature and this transient cooling phenomenon could only appear in the phonon hydrodynamic regime with sufficient normal-process and insufficient resistive-process. In addition, the possibility of this phenomenon observed by experiments is theoretically discussed by using the experimental parameters as the input of the phonon BTE. Results show that this transient cooling phenomenon could obviously appear in a single-layer suspended graphene disk with diameter $7~\mu$m in the temperature range of $50-150$ K. The present work could provide theoretical guidance for the future experimental proof of hydrodynamic phonon transport in two-dimensional materials.