Probing spin and orbital Kondo effects with a mesoscopic interferometer

TL;DR

This paper theoretically explores how spin and orbital Kondo effects influence electron transport in a mesoscopic interferometer with two quantum dots, revealing flux-dependent ground states and Kondo regimes.

Contribution

It introduces a detailed analysis of the transition between SU(4) and SU(2) Kondo states driven by magnetic flux and interdot Coulomb interaction in a double quantum dot system.

Findings

Identification of flux-dependent SU(4) and SU(2) Kondo states.

Demonstration of the crossover between different Kondo regimes.

Prediction of experimental signatures based on magnetic flux variations.

Abstract

We investigate theoretically the transport properties of a closed Aharonov-Bohm interferometer containing two quantum dots in the strong coupling regime. We find two distinct physical scenarios depending on the strength of the interdot Coulomb interaction. When the interdot Coulomb interaction is negligible only spin fluctuations are important and each dot develops a Kondo resonance at the Fermi level independently of the applied magnetic flux. The transport is characterized by the interference of these two independent Kondo resonances. On the contrary, for large interdot interaction, only one electron can be accommodated onto the double dot system. In this situation, not only the spin can fluctuate but also the orbital degree of freedom (the pseudo-spin). As a result, we find different ground states depending on the value of the applied flux. When $\phi=\pi$ (mod $2\pi$) ($\phi=2\pi\Phi/\Phi_0$, where $\Phi$ is applied flux, and $\Phi_0=h/e$ the flux quantum) the electronic transport can take place via simultaneous correlations in the spin and pseudo-spin sectors, leading to the highly symmetric SU(4) Kondo state. Nevertheless, we find situations with $\phi>0$ (mod $2\pi$) where the pseudo-spin quantum number is not conserved during tunneling events, giving rise to the common SU(2) Kondo state with an enhanced Kondo temperature. We investigate the crossover between both ground states and discuss possible experimental signatures of this physics as a function of the applied magnetic flux.