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Enhancement of Andreev reflection by spin polarization in out-of-equilibrium ferromagnet-superconductor junctions

O. Bourgeois·P. Gandit·J. Lesueur·R. Mélin·A. Sulpice·X. Grison·J. Chaussy
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Abstract

We report on transport measurements on Nb/Al/Gd/Al/Nb junctions.Bulk Gadolinium is a weakly polarized ferromagnet (5-7%), and is present in the junction in granular form (superparamagnet). We show that Andreev reflection is strongly enhanced by a weak polarization, obtained by applying an external magnetic field. A new model is proposed that accounts for this effect. The transport is described in terms of ``hot'' carriers that experience Zeeman splitting due to the spin polarized background. The Landauer formula is $G=(4e^2)/h A(h_b)$, $h_b$ being the exchange field at the grain boundary, and A(E) the Andreev current coefficient, that increases with E for resistive junctions.

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O. Bourgeois, P. Gandit, J. Lesueur, R. Mélin, A. Sulpice, X. Grison, J. Chaussy. 1999-01-07. Enhancement of Andreev reflection by spin polarization in out-of-equilibrium ferromagnet-superconductor junctions. https://arxiv.org/abs/cond-mat/9901045

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