Observation of different charge transport regimes and large magnetoresistance in graphene oxide layers

Abstract

We report a systematic study on charge transport properties of thermally reduced graphene oxide (rGO) layers, from room temperature to 2K and in presence of magnetic fields up to 7T. The most conductive rGO sheets follow different transport regimes: at room temperature they show an Arrhenius-like behavior. At lower temperature they exhibits a thermally activated behavior with resistance R following a R=R0exp(T0/T)p law with p=1/3, consistently with 2D Mott Variable Range Hopping (VRH) transport mechanism. Below a given temperature Tc, we observe a crossover from VHR to another regime, probably due to a shortening of the characteristic lengths of the disordered 2D system. The temperature Tc depends on the reduction grade of the rGO. Magnetoresistance ΔR/R of our rGO films shows as well a crossover between positive and negative and below liquid He temperature ΔR/R reaches values larger than ∼–60%, surprisingly high for a – nominally – non magnetic material.