Theoretical study of electronic transport through a small quantum dot with a magnetic impurity

We model a small quantum dot with a magnetic impurity by the Anderson Hamiltonian with a supplementary exchange interaction term. The transport calculations are performed by means of the Green functions within the equation of motion scheme, in which two decoupling procedures are proposed, for high and low temperatures, respectively. The paper focuses on the charge fluctuations for such a system, an aspect not addressed before, as well as on the Kondo resonance. We show a specific role of the excited state, which can be observed in transport and in spin-spin correlations. Our studies show a many-body feature of the phase shift of transmitted electrons, which is manifested in a specific dip. In the Kondo regime, our calculations complement existing theoretical results. The system shows three Kondo peaks in the density of states: one at the Fermi energy and two side peaks, at a distance corresponding to the singlet-triplet level spacing. The existence of the central peak is conditioned by a degenerate state (the triplet) below the Fermi energy.