Effect of electric potential fluctuations in Coulomb drag in double layer graphene systems

We study theoretically the drag transresistivity in a graphene double layer system exhibiting electric potential fluctuations. The fluctuations are modelled as sinusoidal oscillations in the first layer, which induces a sinusoidal variation in the electron density in that layer, which in turn induces an electron density oscillation in the second layer. We calculate the drag resistivity as a function of average charge densities in each layer for various amplitudes of the electric potential fluctuations. Recent experiments have found that the drag transresistivity in graphene double layers systems exhibit a sign change when one layer is held at the charge neutrality point, and the average density of the electrons in the other layer is varied through the charge neutrality point. Our simple model is able to qualitatively reproduce these experimental results. We discuss extensions of the model which characterize more realistically the electric potential fluctuations that are caused by the presence of charge density impurities near the graphene layers.