Andreev Transport through Side-Coupled Double Quantum Dots

TL;DR

This paper investigates how Coulomb interactions and superconducting proximity influence electron transport in side-coupled double quantum dots, revealing enhanced conductance in the Kondo regime and complex Fano interference effects.

Contribution

It provides the first detailed numerical analysis of Andreev transport in side-coupled double quantum dots with superconducting leads, highlighting the interplay between Coulomb interaction, Kondo effect, and superconducting proximity.

Findings

Coulomb interaction suppresses superconducting interference in the side dot.

Superconducting proximity enhances conductance in the Kondo regime.

Two Fano structures emerge in the gate-voltage dependence of Andreev transport.

Abstract

We study the transport through side-coupled double quantum dots, connected to normal and superconducting (SC) leads with a T-shape configuration. We find, using the numerical renormalization group, that the Coulomb interaction suppresses SC interference in the side dot, and enhances the conductance substantially in the Kondo regime. This behavior stands in total contrast to a wide Kondo valley seen in the normal transport. The SC proximity penetrating into the interfacial dot pushes the Kondo clouds, which screens the local moment in the side dot, towards the normal lead to make the singlet bond long. The conductance shows a peak of unitary limit as the cloud expands. Furthermore, two separate Fano structures appear in the gate-voltage dependence of the Andreev transport, where a single reduced plateau appears in the normal transport.