Perturbation treatment for transport through a quantum dot

Resonant tunneling through an Anderson impurity is investigated by employing a perturbation scheme at nonequilibrium. This approach gives the correct weak and strong coupling limit in U by introducing adjustable parameters in the self-energy and imposing self-consistency of the occupation number of the impurity. We have found that the zero-temperature linear-response conductance agrees well with that obtained from the exact sum rule. At finite temperature the conductance shows a nonzero minimum at the Kondo valley, as shown in recent experiments. The effects of an applied bias voltage on the single-particle density of states and on the differential conductances are discussed for Kondo and non-Kondo systems.