Commensurate lattice constant dependent thermal conductivity of misoriented bilayer graphene

Abstract

Misorientation of two layers of bilayer graphene leaves distinct signatures in the electronic properties and the phonon modes. The effect on the thermal conductivity has received the least attention and is the least well understood. In this work, the in-plane thermal conductivity of misoriented bilayer graphene (m-BLG) is investigated as a function of temperature and interlayer misorientation angle using nonequilibrium molecular dynamics (NEMD). The central result is that the calculated thermal conductivities decrease approximately linearly with the increasing lattice constant of the commensurate m-BLG unit cell. Comparisons of the phonon dispersions show that misorientation has negligible affect on the low-energy phonon frequencies and velocities. However, the larger periodicity of m-BLG reduces the Brillouin zone size to the extent that the zone edge acoustic phonons are thermally populated. This allows Umklapp scattering to reduce the lifetimes of the phonons contributing to the thermal transport, and consequently, to reduce the thermal conductivity. This explanation is supported by direct calculation of reduced phonon lifetimes in m-BLG based on density functional theory (DFT).