Heat flow wave in suspended graphene

Abstract

Based on the Guyer–Krumhansl equation, a new form of governing equation for phonon hydrodynamic transport in two-dimensional non-metallic materials is derived, which is only related to heat flux. The solution of this governing equation shows that there is a new wave phenomenon in the phonon hydrodynamic transport, which is called heat flow wave, that is, the damped oscillation of heat flux. The occurrence conditions of the heat flow wave and resonance are analytically deduced. These conditions are different from that of second sound in phonon hydrodynamic transports. The occurrence conditions of the heat flow wave indicate that a small normal scattering time is a necessary condition for the occurrence of the heat flow wave, and the shape and size of suspended graphene have a significant influence on the occurrence of the heat flow wave. It is found that the frequency of the heat flux wave is lower than that of the second sound.