Cross-correlations in a quantum dot Cooper pair splitter with ferromagnetic leads

TL;DR

This paper studies how ferromagnetic leads influence current correlations in a quantum dot Cooper pair splitter, revealing conditions for positive correlations and the impact of ferromagnetism on electron pairing.

Contribution

It introduces a detailed analysis of current cross-correlations in a quantum dot Cooper pair splitter with ferromagnetic leads using real-time diagrammatic techniques.

Findings

Ferromagnetic leads can induce positive current cross-correlations.

Splitted Cooper pairs can produce uncorrelated electrons under certain regimes.

Transport regimes significantly affect current correlation signs.

Abstract

We investigate Andreev transport through a quantum dot attached to two external ferromagnetic leads and one superconducting electrode. The transport properties of the system are studied by means of the real-time diagrammatic technique in the sequential tunneling regime. To distinguish various contributions to Andreev current we calculate the current cross-correlations, i.e. correlations between currents flowing through two junctions with normal leads. We analyze dependence of current cross-correlations on various parameters of the considered model, both in linear and nonlinear transport regimes. The processes and mechanisms leading to enhancement, suppression or sign change of current cross-correlations are examined and discussed. Interestingly, our results show that for specific transport regimes splitted Cooper pair results in two uncorrelated electrons. However, utilizing ferromagnetic leads instead of non-magnetic electrodes can result in positive current cross-correlations.