Structure and transport in multi-orbital Kondo systems

We consider Kondo impurity systems with multiple local orbitals, such as rare earth ions in a metallic host or multi-level quantum dots coupled to metallic leads. It is shown that the multiplet structure of the local orbitals leads to multiple Kondo peaks above the Fermi energy E-F, each one with its own Kondo temperature T-K, and to shadow peaks below E-F. We use a slave boson mean field theory, which recovers the strong coupling Fermi liquid fixed point, to calculate the Kondo peak positions, widths, and heights analytically at T = 0, and NCA calculations to fit the temperature dependence of high-resolution photoemission spectra of Ce compounds. In addition, an approximate conductance quantization for transport through multi-level quantum dots or single-atom transistors in the Kondo regime due to a generalized Friedel sum rule is demonstrated. (C) 2003 Elsevier Science B.V. All rights reserved.