ANDERSON MODEL OUT OF EQUILIBRIUM - NONCROSSING-APPROXIMATION APPROACH TO TRANSPORT THROUGH A QUANTUM-DOT

The infinite-U Anderson model is applied to transport through a quantu m dot. The current and density of states are obtained via the noncross ing approximation for two spin-degenerate levels weakly coupled to two leads. At low temperatures, the Kondo peak in the equilibrium density of states strongly enhances the linear-response conductance. Applicat ion of a finite voltage bias reduces the conductance and splits the pe ak in the density of states. The split peaks, one at each chemical pot ential, are suppressed in amplitude by a finite dissipative lifetime. We estimate this lifetime perturbatively as the time to transfer an el ectron from the higher-chemical-potential lead to the lower-chemical-p otential one. At zero magnetic field, the clearest signatures of the K ondo effect in transport through a quantum dot are the broadening, shi ft, and enhancement of the linear-response conductance peaks at low te mperatures, and a peak in the nonlinear differential conductance aroun d zero bias.