Pseudospin-Resolved Transport Spectroscopy of the Kondo Effect in a Double Quantum Dot

TL;DR

This paper investigates the Kondo effect in a double quantum dot system, revealing pseudospin-resolved transport features and demonstrating the pseudospin character through bias-dependent spectroscopy.

Contribution

It introduces pseudospin-resolved spectroscopy to distinguish pseudospin states and characterizes the Kondo effect in a double quantum dot with differing tunnel rates.

Findings

Zero-bias conductance peak analogous to spin Kondo effect.

Splitting of the Kondo resonance when orbital degeneracy is broken.

Observation of a Kondo peak at only one bias sign, confirming pseudospin resolution.

Abstract

We report measurements of the Kondo effect in a double quantum dot (DQD), where the orbital states act as pseudospin states whose degeneracy contributes to Kondo screening. Standard transport spectroscopy as a function of the bias voltage on both dots shows a zero-bias peak in conductance, analogous to that observed for spin Kondo in single dots. Breaking the orbital degeneracy splits the Kondo resonance in the tunneling density of states above and below the Fermi energy of the leads, with the resonances having different pseudospin character. Using pseudospin-resolved spectroscopy, we demonstrate the pseudospin character by observing a Kondo peak at only one sign of the bias voltage. We show that even when the pseudospin states have very different tunnel rates to the leads, a Kondo temperature can be consistently defined for the DQD system.