Thermal and electrical responses to an external impact in twisted bilayer graphene: excitation strength threshold for angle selectivity

Abstract

Thermal and electrical conductivities are two fundamental features associated with the stochastic transport process of phonons and electrons in a lattice system. Twisted bilayer graphene has attracted enormous attention in recent years as a material of correlated quantum phases; however, its thermal and electrical transport behavior in response to a strong external impact is still unclear. In this paper, we show that, under strong external out-of-plane thermal excitation, the spreading of thermal and electrical potential energy in a twisted bilayer graphene is insensitive to its twist angle at a considerable wide range until an excitation strength threshold, using a large-scale ab initio nonequilibrium molecular dynamics simulation involving thousands of atoms. To understand the microscopic mechanism, the portion of energy between the flexural and planar modes is calculated. It is found that before the excitation strength threshold, a large portion of energy is distributed to the flexural mode whose transport is insensitive to interlayer interactions. By crossing the excitation strength threshold at a twisted angle that is near the AB-stacked configuration, more energy is distributed to the planar mode, which breaks the carbon covalent bonds and facilitates the formation of a 5-7-7-5 ring defective structure. It also results in a higher spreading speed of thermal and electrical responses, particularly the electrical response, in the bilayer graphene at the twisted angle near the AB-stacked configuration compared to the AA-stacked configuration. The higher electrical conductivity of the defective structure is further evidenced by comparing its density of states with that of the pristine structure. Our findings provide an insight into the complex transport behavior of thermal and electrical potential energy in twisted bilayer graphene and offer a promising method for designing adjustable thermal and thermoelectric devices.