Nonequilibrium Kondo Effect in a Multi-level Quantum Dot near singlet-triplet transition

TL;DR

This paper investigates the nonequilibrium Kondo effect in a multi-level quantum dot near singlet-triplet transition, revealing conductance enhancements, non-monotonic temperature dependence, and interference effects between energy levels.

Contribution

It introduces a generalized finite-U slave-boson mean field approach to analyze transport in multi-level quantum dots, highlighting a two-stage Kondo effect near singlet-triplet degeneracy.

Findings

Conductance enhancement near singlet-triplet degeneracy

Non-monotonic temperature dependence of conductance

Interference between energy levels causes a two-stage Kondo effect

Abstract

The linear and nonlinear transport through a multi-level lateral quantum dot connected to two leads is investigated using a generalized finite-$U$ slave-boson mean field approach. For a two-level quantum dot, our calculation demonstrates a substantial conductance enhancement near the degeneracy point of the spin singlet and triplet states, a non-monotonic temperature-dependence of conductance and a sharp dip and nonzero bias maximum of the differential conductance. These agree well with recent experiment observations. This two-stage Kondo effect in an out-of-equilibrium situation is attributed to the interference between the two energy levels.