Thermal rectification induced by phonon hydrodynamics in asymmetric 2D microstructures

Abstract

A thermal diode/rectifier, where the thermal resistance is direction dependent, has always been highly sought after and may find applications in potential thermal logic devices and thermal management systems. By using a more accurate local spatial linear approximation (LSLA) when numerically solving the phonon Boltzmann transport equation (BTE) under Callaway's dual model, it is shown here for the first time that phonon hydrodynamics combined with geometric asymmetry can lead to thermal rectification (TR). Interestingly, in a T-shaped graphene microribbon heat preferentially flows from the narrow end to the wide end, which is opposite to what is observed in T-shaped graphene nanoribbons. Flexural acoustic (ZA) phonons play the dominant role in the TR effect, due to their prominent hydrodynamic behavior. By analysis of the temperature spatial distribution and the phonon mean free paths (MFP), the reasons for TR are explained. By adjusting geometric parameters, the 16 % TR ratio is reached. Furthermore, the impact of edge roughness, temperature difference and strength of phonon hydrodynamics on the TR effect are investigated. This work points to a new mechanism for enabling thermal rectification and may provide insight into the unique interplay between phonon hydrodynamics and engineered microstructures.