▎ 摘　　要

Using molecular dynamics simulations, we create an unprecedented scenario in graphene nanoribbons: co-existence of two heat currents in opposite directions at the same location. One heat current is carried by flexural mode phonons, and the other one by transverse/longitudinal modes phonons in the opposite direction. The local apparent thermal conductivity (kappa(app)) varies in a very large range: -468 to 1434 W/m K. The negative kappa(app) does not violate the second law of thermodynamics. It is a combined effect of the much higher thermal conductivity of flexural mode phonons and the weak coupling between them and transverse/longitudinal modes phonons. (C) 2013 Elsevier B.V. All rights reserved.