ELECTRON-TRANSPORT THROUGH SMALL QUANTUM DOTS - ZERO-BIAS ANOMALIES AND MAGNETIC-FIELD DEPENDENCE

We study resonant tunneling through a single-level quantum dot in the presence of strong Coulomb repulsion. Tile level is either spin-degene rate or split by a magnetic field. Using a real-time diagrammatic form ulation we calculate the spectral density and the nonlinear I-V charac teristic. The former shows Kondo peaks split by the transport voltage. This leads to zero-bias anomalies in the differential conductance, wh ich agree well with recent experiments on single-charge traps. Further more, we predict that the sign of the zero-bias anomaly depends on the level position relative to tile Fermi level of the leads.