Andreev Reflection In Ferromagnet-Superconductor Junctions

TL;DR

This paper investigates how Andreev reflection influences transport in ferromagnet-superconductor junctions, revealing effects of exchange interaction and tunnel barriers on conductance, with implications for understanding spin-polarized transport.

Contribution

It introduces a scattering formulation to analyze the impact of exchange interaction and tunnel barriers on conductance in FS junctions, highlighting novel resonance phenomena.

Findings

Conductance can be enhanced or suppressed depending on exchange and Fermi energy ratios.

Resonances in conductance persist in linear response due to tunnel barriers.

Andreev reflection is significantly affected by ferromagnetic exchange interactions.

Abstract

The transport properties of a ferromagnet-superconductor (FS) junction are studied in a scattering formulation. Andreev reflection at the FS interface is strongly affected by the exchange interaction in the ferromagnet. The conductance G_FS of a ballistic point contact between F and S can be both larger or smaller than the value G_FN with the superconductor in the normal state, depending on the ratio of the exchange and Fermi energies. If the ferromagnet contains a tunnel barrier (I), the conductance G_FIFS exhibits resonances which do not vanish in linear response -- in contrast to the Tomasch oscillations for non-ferromagnetic materials.