Gate-tunable acoustoelectric effect in graphene

Piezoelectric surface acoustic waves (SAWs) are a sensitive contact-less probe for studying the electronic properties of two dimensional electron systems. We demonstrate gate-tunable acoustoelectric transport in exfoliated graphene by measuring the voltage created as SAWs dynamically drive charge carriers in the graphene. We employ a flip-chip configuration to conduct acoustoelectric measurements while simultaneously varying the graphene carrier density with a back-gate. At high carrier density we observe dependence of the acoustoelectric signal on the sign of the charge carriers, while at low densities we observe anomalous sign reversals of the acoustically generated voltage. We attribute these anomalous sign reversals to spatially heterogeneous conduction in the vicinity of charge neutrality.