Johannes Kern, Milena Grifoni
We describe linear and nonlinear transport across a single impurity Anderson model quantum dot with intermediate coupling to the leads. The coupling is large enough that sequential tunneling processes alone do not suffice to properly describe the transport characteristics. Upon applying a density matrix approach, the current is expressed in terms of rates obtained by considering a very small class of diagrams which dress the sequantial tunneling processes by charge fluctuations. We find zero bias anomalies of the differential conductance versus applied bias, an enhancement of the conductance with decreasing temperature as well as the onset of universality of the shape of the conductance as function of the temperature. We can address the case of a spin-degenerate level split energetically by a magnetic field and show that, if we assume in addition different capacitive couplings of the two spin-levels to the leads, one of the resonance peaks is vanishing. Furthermore, we get qualitative agreement with experimental data showing a cross-over from the Kondo to the empty orbital regime.
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http://arxiv.org/abs/1209.4995
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