arXiv subjects
Publications and source records attributed to O. Bourgeois.
We consider Andreev reflection in ferromagnet-superconductor junctions and extend the treatment by de Jong and Beenakker to incorporate the effect of a repulsive potential at the interface. We show the existence of a spin accumulation at a finite voltage in this model.
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.