▎ 摘　　要

A physical model is proposed to clarify the electron transport through graphene-metal interfaces. It is based on an effective description of the coupling between the graphene pi-bands and the metal sd- and d-bands. Applying this model to vertically symmetrical metal-graphene-metal structures, we show that the current-voltage characteristics can be either linear or non-linear with a negative or positive differential resistance depending on the dominance of the d-like or s-like electrons in the metal as well as the graphene-metal coupling. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4761940]