Structure and transport in multi-orbital Kondo systems

TL;DR

This paper investigates multi-orbital Kondo systems, revealing multiple Kondo peaks and shadow features, and provides analytical and numerical insights into their spectral and transport properties.

Contribution

It introduces a theoretical framework for understanding multiple Kondo peaks in multi-orbital systems and demonstrates conductance quantization due to a generalized Friedel sum rule.

Findings

Multiple Kondo peaks above and below Fermi energy identified.

Analytical expressions for peak positions, widths, and heights derived.

Approximate conductance quantization demonstrated in multi-level quantum dots.

Abstract

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 $E_F$, 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.