Spin-dependent transport through graphene quantum dots

We analyze theoretically transport properties of graphene quantum dots weakly coupled to normal and ferromagnetic leads. The calculations are performed by using the real-time diagrammatic technique in the first-order approximation with respect to tunneling processes. First, we analyze the energy spectrum of graphene dots of different shape. Then, we determine the current flowing through the system and the differential conductance. We show that the structure of the Coulomb diamonds of graphene quantum dots greatly depends on energy spectrum and therefore on the shape of the dots. In the case of ferromagnetic leads we also determine the tunnel magnetoresistance, which displays a nontrivial behavior depending on the number of charge states taking part in transport, and on particular shape of the graphene flake.