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 EF, each one with its own Kondo temperature TK, and to “shadow” peaks below EF. 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.