Phonon transport on two-dimensional graphene/boron nitride superlattices

Using nonequilibrium molecular dynamics and lattice dynamics, we investigate phonon conduction on two-dimensional graphene/boron nitride superlattices with varying periods and interface structures. As the period of superlattice increases to a critical value near 5 nm the lattice thermal conductivity drops sharply to a minimum, and beyond that it smoothly increases with the period. We show that the minimum in the thermal conductivity arises from a competition between lattice dispersion and anharmonic effects such as interface scattering. The initial reduction of thermal conductivity can partially be accounted for by harmonic wave effects induced by interfacial modulation, such as the opening of phononic band gaps and reduction of group velocity. Beyond the minimum, reduced inelastic interface scattering is responsible for the recovery. The overall range of thermal conductivity exhibited by the superlattices is substantially reduced with respect to the parent materials. A universal scaling of the thermal conductivity with total superlattice length is found, suggesting that the critical period is independent of total length and that long-wavelength phonons are dominant carriers. Furthermore, we demonstrate the ultrasensitivity of thermal conductivity to interfacial defects and superlattice periodicity disorder.