Nonlocal Andreev Reflections as a Source of Spin Exchange and Kondo Screening

TL;DR

This paper introduces a new exchange mechanism mediated by nonlocal Andreev reflections in a double quantum dot system near a superconductor, affecting Kondo screening and low-temperature transport.

Contribution

It presents the first detailed analysis of superconductor-induced exchange leading to two-stage Kondo screening, combining analytical and numerical methods.

Findings

Superconductor-induced exchange causes two-stage Kondo screening.

Kondo temperature depends on superconductor coupling.

Distinct low-temperature transport signatures predicted.

Abstract

We report on a novel exchange mechanism, mediating the Kondo screening, in a correlated double quantum dot structure in the proximity of superconductor, stemming from nonlocal Andreev reflection processes. We estimate its strength perturbatively and corroborate analytical predictions with accurate numerical renormalization group calculations using an effective model for the superconductor-proximized nanostructure. We demonstrate that superconductor-induced exchange leads to a two-stage Kondo screening. We determine the dependence of the Kondo temperature on the coupling to superconductor and predict a characteristic modification of conventional low-temperature transport behavior, which can be used to experimentally distinguish this phenomenon from other Kondo effects.