Thermoelectric transport through interacting quantum dots in graphene

Abstract

We study the thermoelectric properties of an electronic localized level coupled to two graphene electrodes. Graphene band structure shows a pseudogap density of states (DOS) that strongly affects the charge transport. We focus on the Coulomb blockade regime and derive the expression for the Onsager matrix that relates the charge and heat currents to the voltage and temperature biases in the linear response regime. The elements of the Onsager matrix are functions of the transmission coefficient, which depends on the dot Green’s function. Our self-consistent calculation of the Green’s function is based on the equation-of-motion technique. We find a double-peak structure for the electric and thermal responses as the dot level is tuned with an external gate terminal, in accordance with the Coulomb blockade phenomenon. Remarkably enough, the thermal conductance is much smaller than its electric counterpart, giving rise to a high thermoelectric figure of merit for certain values of the gate voltage. Finally, we discuss a large departure from the Wiedemann–Franz law caused mainly by the pseudogap DOS in the contacts and weakly affected by interactions.