Superconducting proximity effect in interacting double-dot systems

TL;DR

This paper investigates how superconducting correlations influence electron transport in a double quantum dot system with strong Coulomb repulsion, revealing asymmetric current-voltage behavior and tunable Andreev excitation splitting.

Contribution

It provides new insights into non-local superconducting effects and control of Andreev states in interacting double-dot systems, which were not previously characterized.

Findings

Asymmetric I-V characteristics due to spin state incompatibility.

Gate-tunable splitting of Andreev excitation energies.

Detection of non-local superconducting correlations via conductance measurements.

Abstract

We study subgap transport from a superconductor through a double quantum dot with large on-site Coulomb repulsion to two normal leads. Non-local superconducting correlations in the double dot are induced by the proximity to the superconducting lead, detectable in non-local Andreev transport that splits Cooper pairs in locally separated, spin-entangled electrons. We find that the $I$--$V$ characteristics are strongly asymmetric: for a large bias voltage of certain polarity, transport is blocked by populating the double dot with states whose spin symmetry is incompatible with the superconductor. Furthermore, by tuning gate voltages one has access to splitting of the Andreev excitation energies, which is visible in the differential conductance.