Generation of pure spin currents by superconducting proximity effect in quantum dots

TL;DR

This paper demonstrates how a three-terminal quantum dot system can generate pure spin currents through non-equilibrium superconducting proximity effects, tunable by gate voltage, despite Coulomb blockade effects.

Contribution

It reveals a novel mechanism for pure spin current generation in quantum dots via interplay of Andreev reflection and spin accumulation, controlled by gate tuning.

Findings

Pure spin currents can be generated without charge flow.

Non-equilibrium proximity effect enhances Andreev current.

Gate voltage controls spin current generation.

Abstract

We investigate electronic transport in a three-terminal hybrid system, composed by an interacting quantum dot tunnel coupled to one superconducting, one ferromagnetic, and one normal lead. Despite the tendency of the charging energy to suppress the superconducting proximity effect when the quantum dot is in equilibrium, the non-equilibrium proximity effect can give rise to a large Andreev current. The presence of the ferromagnet can lead to a finite spin accumulation on the dot. We find that the interplay of the Andreev current and spin accumulation can generate a pure spin current, with no associated charge transport, in the normal lead. This situation is realised by tuning the quantum-dot spectrum by means of a gate voltage.