Andreev magnetotransport in low-dimensional proximity structures: Spin-dependent conductance enhancement

We study the excess conductance due to the superconducting proximity effect in a ballistic two-dimensional electron system subject to an in-plane magnetic field. We show that under certain conditions the interplay of the Zeeman spin splitting and the effect of a screening supercurrent gives rise to a spin-selective Andreev enhancement of the conductance and anomalies in its voltage, temperature and magnetic field characteristics. The magnetic-field influence on Andreev reflection is discussed in the context of using superconducting hybrid junctions for spin detection.Comment: 4 pages, 5 figure

Ladungstransport an Grenzflaechen zwischen Supraleitern und hochbeweglichen zweidimensionalen Elektronengasen

From scientific point of view as well as with regard to possible applications in superconducting electronics it is interesting to combine quantum effects and ballistic transport in semiconductors with the superconducting state. Due to the high mobility and long de Broglie wave length of the charge carriers, two-dimensional electron gases (2DEG) are suitable for observing the mentioned effects. Therefore, in this work basic investigations of single superconductor/2DEG contacts are presented. The high-mobility 2DEG used in this work forms at the interface of a GaInAs/InP heterostructure. As contact materials the superconductors Nb and NbN as well as the normal metals Au and Co are used. In addition to these mainly technological investigations, measurements of the normal state resistance of Nb/2DEG contacts in a magnetic field are presented. If the magnetic field is orientated perpendicular to the plane of the 2DEG, the normal state contact resistance drops dramatically with increasing magnetic field. This decrease is explained in terms of a model which assumes ballistic transport in the 2DEG. Having this model in hand, transport near the interface as well as the properties of the contact can be characterized in more detail. A new effect in the differential resistance of NbN/2DEG contacts in magnetic fields perpendicular to the plane of the 2DEG has been observed. This effect manifests itself in a splitting of the usual resistance maximum into a three-fold structure at voltages lower than the superconducting gap voltage. (orig.)129 refs.Available from TIB Hannover: RA 831(3490) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman