Time-resolved charge detection in graphene quantum dots

We present real-time detection measurements of electron tunneling in a graphene quantum dot. By counting single-electron charging events on the dot, the tunneling process in a graphene constriction and the role of localized states are studied in detail. In the regime of low charge detector bias we see only a single time-dependent process in the tunneling rate which can be modeled using a Fermi-broadened energy distribution of the carriers in the lead. We find a nonmonotonic gate dependence of the tunneling coupling attributed to the formation of localized states in the constriction. Increasing the detector bias above Vb=2 mV results in an increase of the dot-lead transition rate related to back action of the charge detector current on the dot.