Theoretical studies of transient hydrodynamic phonon transport in two-dimensional disk geometry

Abstract

Many phonon hydrodynamics phenomena, including heat vortices, wave and parabolic distributions of heat flux, which appear due to sufficient normal process, can also appear when there is insufficient normal process. In other words, a smoking gun of phonon hydrodynamics phenomena at the macroscopic level is still lacking. To find it, transient cooling phenomenon in two-dimensional materials is studied based on the phonon Boltzmann transport equation. A heating pulsed Gaussian laser beam is added at the center of two-dimensional disk and it continues to heat the system for a while under the environment temperature. After the heating laser is removed, results show that the transient temperature could be lower than the environment temperature and this phenomenon could only appear with sufficient normal process and insufficient resistive process, which is exactly a smoking gun of phonon hydrodynamics. In addition, the possibility of this phenomenon measured by transient Raman experiments is theoretically discussed. Numerical results show that given a single-layer suspended graphene disk sample with diameter 7 μm, this transient cooling phenomenon can appear in the temperature range of 50–150 K.