Manifestation of the shape and edge effects in spin-resolved transport through graphene quantum dots

We report on theoretical studies of transport through graphene quantum dots weakly coupled to external ferromagnetic leads. The calculations are performed by exact diagonalization of a tight-binding Hamiltonian with finite Coulomb correlations for graphene sheet and by using the real-time diagrammatic technique in the sequential and cotunneling regimes. The emphasis is put on the role of graphene flake shape and spontaneous edge magnetization in transport characteristics, such as the differential conductance, tunneling magnetoresistance (TMR), and the shot noise. It is shown that for certain shapes of the graphene dots, a negative differential conductance and nontrivial behavior of the TMR effect can occur.