Characteristics of acoustic phonon transport and thermal conductance in multi-terminal graphene junctions

Abstract

By using non-equilibrium Greens function method, we investigate the transmission rate of acoustic phonon and thermal conductance through a parallel multi-terminal graphene junctions, the relationship between the thermal-transport property in each terminal and the number of quantum terminals, the relationship between the thermal-transport property in each terminal and the relative position of quantum terminals in quantum structure, and also study the thermaltransport property in each terminal and the rough degree of edge structure. The results show that when the graphene chains (dimer lines) across the ribbon width are fixed, the increase of the number of the parallel multi-terminal graphene junctions can reduce the transmission rate of the phonons and the thermal conductance of each output terminal as well. This is because the increase of the number of the graphene junctions can lead to the decrease of the transverse dimension of the each output terminal, which enlarges the strength of the phonon scattering and results in the reduction of the phonon transmission. Owing to long distance scattering, the transmission rate of the phonons of the furthest distant output terminal is the smallest, and also the thermal conductance of the furthest output terminal is the smallest. On the contrary, the strength of the phonon scattering is the weakest for the closest output terminal. So the transmission rate of the phonons is the biggest, which induces the thermal conductance to be the biggest. The thermal conductance of the middle-output terminal depends sensitively on the structural parameters of each terminal. This is because mainly the relative position between the middle-output terminal and the phonon-input terminal is related closely to the structural parameters of each terminal, which can influence the strength of the phonon scattering and the transmission rate of the phonons. However, the thermal conductances in the top and bottom output terminals are just sensitively dependent on the structural parameters of the respective output terminal. This is because the relative position between the top (or bottom) output terminal and the phonon-input terminal is only related to the structural parameters of the respective output terminal. The rough edge structure can reduce obviously the transmission rate of the phonons, and the thermal conductance of the closest output terminal as well. The rough edge structure can modulate slightly the transmission rate of the phonons and the thermal conductance of the other output terminal. The total thermal conductance is related closely to the number of total graphene chains, the number of the multi-terminal graphene junctions, and the rough degree of edge structure. These results shed new light on the understanding of the thermal transport behaviors of multi-terminal junction quantum devices based on graphene-based nanomaterials in practical application.