Nonequilibrium transport through parallel double quantum dots in the Kondo regime

TL;DR

This paper develops a perturbative nonequilibrium renormalization group method to study transport in double quantum dots, revealing Kondo peaks, negative differential conductance, and criteria to differentiate spin and orbital Kondo effects.

Contribution

It introduces a novel perturbative approach for multi-orbital systems and applies it to analyze complex transport phenomena in double quantum dots.

Findings

Kondo peaks appear at three voltages in conductance.

Disappearance of a Kondo peak when one dot is decoupled.

Negative differential conductance observed with asymmetric lead coupling.

Abstract

We extend a perturbative, nonequilibrium renormalization group approach to multi-orbital systems and apply it for studying transport through two parallel quantum dots coupled electrostatically. In general, the conductance shows pronounced Kondoesque peaks at three voltages. One of these peaks disappears if, as in some experiments, one of the dots is decoupled from one of the two leads. For an asymmetric coupling to the leads, also negative differential conductances are possible. This is a genuine nonequilibrium effect, accompanying the Kondoesque peaks. Moreover, a criterion to distinguish spin and orbital Kondo effect in such a system is discussed.