Publication date: 8th January 2019
We theoretically analyze the transport properties of a single electron transistor made of a quantum dot coupled to pure monolayer graphene source and drain electrodes. We apply an asymmetric bias voltage to the graphene leads and consider a metallic gate electrode. We employ the pseudogap Anderson Hamiltonian [1] in order to describe the system and use the equation-of-motion technique with the Meir approximation [2] within the Lacroix decoupling scheme [3] to determine the retarded Green's function for the dot. The Coulomb interaction between localized electrons in the dot is assumed to be finite. We find that the transition from the Coulomb blockade regime to the Kondo regime in the transport through the dot takes place when the coupling strength between the dot and graphene leads is continuously increased. The current-voltage characteristic for the quantum dot within the Coulomb blockade regime contains two steps. The appearance of these steps is caused by the changing number of electrons in the dot. The positions of steps are determined by the single energy level and the Coulomb interaction of localized electrons in dot. The discrete energy level can be tuned by the gate voltage through the gate electrode. In our graphene-based system, contrary to theoretical studies for quantum dots with metallic leads [2,4], the strongly temperature dependent Kondo resonances appear in the density of states only at the nonzero chemical potentials. Therefore, the zero-bias peak in the differential conductance does not rise up for zero value of the fixed chemical potential due to the linear energy dispersion of the graphene leads.
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