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

¹ Theoretische Physik, Universität Duisburg-Essen and CeNIDE - 47048 Duisburg, Germany, EU
² School of Chemical and Physical Sciences and MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington - PO Box 600, Wellington, New Zealand

^a david@thp.uni-due.de

Received: 27 May 2010
Accepted: 2 August 2010

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.