  In this paper, heat flux in graphene nano ribbons has been studied by using
molecular dynamics simulations. It is found that the heat flux runs
preferentially along the direction of decreasing width, which demonstrates
significant thermal rectification effect in the asymmetric graphene ribbons.
The dependence of rectification ratio on the vertex angle and the length are
also discussed. Compared to the carbon nanotube based one-dimensional thermal
rectifier, graphene nano ribbons have much higher rectification ratio even in
large scale. Our results demonstrate that asymmetric graphene ribbon might be a
promising structure for practical thermal (phononics) device.
