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Graphene is an attractive electrode material to contact nanostructures downto the molecular scale since it can be gated electrostatically. Gating can beused to control the doping and the energy level alignment in the nanojunction,thereby influencing its conductance. Here we investigate the impact ofelectrostatic gating in nanojunctions between graphene electrodes operating atfinite bias. Using first principles quantum transport simulations, we show thatthe voltage drop across \emph{symmetric} junctions changes dramatically andcontrollably in gated systems compared to non-gated junctions. In particular,for \emph{p}-type(\emph{n}-type) carriers the voltage drop is located close tothe electrode with positive(negative) polarity, i.e. the potential of thejunction is pinned to the negative(positive) electrode. We trace this behaviourback to the vanishing density of states of graphene in the proximity of theDirac point. Due to the electrostatic gating, each electrode exposes differentdensity of states in the bias window between the two different electrode Fermienergies, thereby leading to a non-symmetry in the voltage drop across thedevice. This selective pinning is found to be independent of device length whencarriers are induced either by the gate or dopant atoms, indicating a generaleffect for electronic circuitry based on graphene electrodes. We envision thiscould be used to control the spatial distribution of Joule heating in graphenenanostructures, and possibly the chemical reaction rate around high potentialgradients.

Manipulating the voltage drop in graphene nanojunctions using a gate potential