Kondo effect in a quantum dot with even number of electrons: zero-bandwidth approach

The zero-bandwidth limit of the Anderson model is applied to calculate the electrical transport properties through a semiconductor quantum dot, focusing on the regime with two localized electrons inside the dot. The model includes two localized orbitals in the dot, with intra-orbital and inter-orbital Coulomb repulsion energies, coupled to two leads with different electrochemical potentials. We take symmetric hybridization strength (equal couplings between dot and left and right leads) and we consider the exchange energy between two localized electrons in the dot. Magnetic field effects are included by assuming that it produces a splitting in the one-particle energy levels. We study manifestations of the integer-spin Kondo effect in equilibrium (linear-response conductance) and non-equilibrium (differential conductance) properties. The results are directly related and in good qualitative agreement with recent experimental data.