Restoring the SU(4) Kondo regime in a double quantum dot system

TL;DR

This paper demonstrates that in a double quantum dot system, the SU(4) Kondo regime can be effectively restored by tuning the level difference, despite asymmetries in coupling to leads, aiding experimental detection of SU(4) symmetry.

Contribution

The study shows that SU(4) Kondo symmetry can be recovered in asymmetric double quantum dots by adjusting the level difference, extending understanding of symmetry control in quantum dot systems.

Findings

SU(4) symmetry is recoverable by tuning level difference.

System exhibits SU(4) Kondo behavior at low energies.

Asymmetries in coupling can be compensated by level tuning.

Abstract

We calculate the spectral density and occupations of a system of two capacitively coupled quantum dots, each one connected to its own pair of conducting leads, in a regime of parameters in which the total coupling to the leads for each dot $\Gamma_i$ are different. The system has been used recently to perform pseudospin spectroscopy by controlling independently the voltages of the four leads. For an odd number of electrons in the system, $\Gamma_1=\Gamma_2$, equal dot levels $E_1=E_2$ and sufficiently large interdot repulsion $U_{12}$ the system lies in the SU(4) symmetric point of spin and pseudospin degeneracy in the Kondo regime. In the more realistic case $\Gamma_1 \neq \Gamma_2$, pseudospin degeneracy is broken and the symmetry is reduced to SU(2). Nevertheless we find that the essential features of the SU(4) symmetric case are recovered by appropriately tuning the level difference $\delta=E_2-E_1$. The system behaves as an SU(4) Kondo one at low energies. Our results are relevant for experiments which look for signatures of SU(4) symmetry in the Kondo regime of similar systems.